| Message ID | 20220530202711.2594486-1-davemarchevsky@fb.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | [v4,bpf-next,1/2] selftests/bpf: Add benchmark for local_storage get | expand |
On Mon, May 30, 2022 at 1:27 PM Dave Marchevsky <davemarchevsky@fb.com> wrote: > > Add a benchmarks to demonstrate the performance cliff for local_storage > get as the number of local_storage maps increases beyond current > local_storage implementation's cache size. > > "sequential get" and "interleaved get" benchmarks are added, both of > which do many bpf_task_storage_get calls on sets of task local_storage > maps of various counts, while considering a single specific map to be > 'important' and counting task_storage_gets to the important map > separately in addition to normal 'hits' count of all gets. Goal here is > to mimic scenario where a particular program using one map - the > important one - is running on a system where many other local_storage > maps exist and are accessed often. > > While "sequential get" benchmark does bpf_task_storage_get for map 0, 1, > ..., {9, 99, 999} in order, "interleaved" benchmark interleaves 4 > bpf_task_storage_gets for the important map for every 10 map gets. This > is meant to highlight performance differences when important map is > accessed far more frequently than non-important maps. > > A "hashmap control" benchmark is also included for easy comparison of > standard bpf hashmap lookup vs local_storage get. The benchmark is > identical to "sequential get", but creates and uses BPF_MAP_TYPE_HASH > instead of local storage. > > Addition of this benchmark is inspired by conversation with Alexei in a > previous patchset's thread [0], which highlighted the need for such a > benchmark to motivate and validate improvements to local_storage > implementation. My approach in that series focused on improving > performance for explicitly-marked 'important' maps and was rejected > with feedback to make more generally-applicable improvements while > avoiding explicitly marking maps as important. Thus the benchmark > reports both general and important-map-focused metrics, so effect of > future work on both is clear. > > Regarding the benchmark results. On a powerful system (Skylake, 20 > cores, 256gb ram): > > Local Storage > ============= > Hashmap Control w/ 500 maps > hashmap (control) sequential get: hits throughput: 48.338 ± 2.366 M ops/s, hits latency: 20.688 ns/op, important_hits throughput: 0.097 ± 0.005 M ops/s > > num_maps: 1 > local_storage cache sequential get: hits throughput: 44.503 ± 1.080 M ops/s, hits latency: 22.470 ns/op, important_hits throughput: 44.503 ± 1.080 M ops/s > local_storage cache interleaved get: hits throughput: 54.963 ± 0.586 M ops/s, hits latency: 18.194 ns/op, important_hits throughput: 54.963 ± 0.586 M ops/s > > num_maps: 10 > local_storage cache sequential get: hits throughput: 43.743 ± 0.418 M ops/s, hits latency: 22.861 ns/op, important_hits throughput: 4.374 ± 0.042 M ops/s > local_storage cache interleaved get: hits throughput: 50.073 ± 0.609 M ops/s, hits latency: 19.971 ns/op, important_hits throughput: 17.883 ± 0.217 M ops/s > > num_maps: 16 > local_storage cache sequential get: hits throughput: 43.962 ± 0.525 M ops/s, hits latency: 22.747 ns/op, important_hits throughput: 2.748 ± 0.033 M ops/s > local_storage cache interleaved get: hits throughput: 48.166 ± 0.825 M ops/s, hits latency: 20.761 ns/op, important_hits throughput: 15.326 ± 0.263 M ops/s > > num_maps: 17 > local_storage cache sequential get: hits throughput: 33.207 ± 0.461 M ops/s, hits latency: 30.114 ns/op, important_hits throughput: 1.956 ± 0.027 M ops/s > local_storage cache interleaved get: hits throughput: 43.540 ± 0.265 M ops/s, hits latency: 22.968 ns/op, important_hits throughput: 13.255 ± 0.081 M ops/s > > num_maps: 24 > local_storage cache sequential get: hits throughput: 19.402 ± 0.348 M ops/s, hits latency: 51.542 ns/op, important_hits throughput: 0.809 ± 0.015 M ops/s > local_storage cache interleaved get: hits throughput: 22.981 ± 0.487 M ops/s, hits latency: 43.514 ns/op, important_hits throughput: 6.465 ± 0.137 M ops/s > > num_maps: 32 > local_storage cache sequential get: hits throughput: 13.378 ± 0.220 M ops/s, hits latency: 74.748 ns/op, important_hits throughput: 0.419 ± 0.007 M ops/s > local_storage cache interleaved get: hits throughput: 16.894 ± 0.172 M ops/s, hits latency: 59.193 ns/op, important_hits throughput: 4.716 ± 0.048 M ops/s > > num_maps: 100 > local_storage cache sequential get: hits throughput: 6.070 ± 0.140 M ops/s, hits latency: 164.745 ns/op, important_hits throughput: 0.061 ± 0.001 M ops/s > local_storage cache interleaved get: hits throughput: 7.323 ± 0.149 M ops/s, hits latency: 136.554 ns/op, important_hits throughput: 1.913 ± 0.039 M ops/s > > num_maps: 1000 > local_storage cache sequential get: hits throughput: 0.438 ± 0.012 M ops/s, hits latency: 2281.369 ns/op, important_hits throughput: 0.000 ± 0.000 M ops/s > local_storage cache interleaved get: hits throughput: 0.522 ± 0.010 M ops/s, hits latency: 1913.937 ns/op, important_hits throughput: 0.131 ± 0.003 M ops/s > > Looking at the "sequential get" results, it's clear that as the > number of task local_storage maps grows beyond the current cache size > (16), there's a significant reduction in hits throughput. Note that > current local_storage implementation assigns a cache_idx to maps as they > are created. Since "sequential get" is creating maps 0..n in order and > then doing bpf_task_storage_get calls in the same order, the benchmark > is effectively ensuring that a map will not be in cache when the program > tries to access it. > > For "interleaved get" results, important-map hits throughput is greatly > increased as the important map is more likely to be in cache by virtue > of being accessed far more frequently. Throughput still reduces as # > maps increases, though. > > To get a sense of the overhead of the benchmark program, I > commented out bpf_task_storage_get/bpf_map_lookup_elem in > local_storage_bench.c and ran the benchmark on the same host as the > 'real' run. Results: > > Local Storage > ============= > Hashmap Control w/ 500 maps > hashmap (control) sequential get: hits throughput: 96.965 ± 1.346 M ops/s, hits latency: 10.313 ns/op, important_hits throughput: 0.194 ± 0.003 M ops/s > > num_maps: 1 > local_storage cache sequential get: hits throughput: 105.792 ± 1.860 M ops/s, hits latency: 9.453 ns/op, important_hits throughput: 105.792 ± 1.860 M ops/s > local_storage cache interleaved get: hits throughput: 185.847 ± 4.014 M ops/s, hits latency: 5.381 ns/op, important_hits throughput: 185.847 ± 4.014 M ops/s > > num_maps: 10 > local_storage cache sequential get: hits throughput: 109.867 ± 1.358 M ops/s, hits latency: 9.102 ns/op, important_hits throughput: 10.987 ± 0.136 M ops/s > local_storage cache interleaved get: hits throughput: 144.165 ± 1.256 M ops/s, hits latency: 6.936 ns/op, important_hits throughput: 51.487 ± 0.449 M ops/s > > num_maps: 16 > local_storage cache sequential get: hits throughput: 109.258 ± 1.902 M ops/s, hits latency: 9.153 ns/op, important_hits throughput: 6.829 ± 0.119 M ops/s > local_storage cache interleaved get: hits throughput: 140.248 ± 1.836 M ops/s, hits latency: 7.130 ns/op, important_hits throughput: 44.624 ± 0.584 M ops/s > > num_maps: 17 > local_storage cache sequential get: hits throughput: 116.397 ± 7.679 M ops/s, hits latency: 8.591 ns/op, important_hits throughput: 6.856 ± 0.452 M ops/s > local_storage cache interleaved get: hits throughput: 128.411 ± 4.927 M ops/s, hits latency: 7.787 ns/op, important_hits throughput: 39.093 ± 1.500 M ops/s > > num_maps: 24 > local_storage cache sequential get: hits throughput: 110.890 ± 0.976 M ops/s, hits latency: 9.018 ns/op, important_hits throughput: 4.624 ± 0.041 M ops/s > local_storage cache interleaved get: hits throughput: 133.316 ± 1.889 M ops/s, hits latency: 7.501 ns/op, important_hits throughput: 37.503 ± 0.531 M ops/s > > num_maps: 32 > local_storage cache sequential get: hits throughput: 112.900 ± 1.171 M ops/s, hits latency: 8.857 ns/op, important_hits throughput: 3.534 ± 0.037 M ops/s > local_storage cache interleaved get: hits throughput: 132.844 ± 1.207 M ops/s, hits latency: 7.528 ns/op, important_hits throughput: 37.081 ± 0.337 M ops/s > > num_maps: 100 > local_storage cache sequential get: hits throughput: 110.025 ± 4.714 M ops/s, hits latency: 9.089 ns/op, important_hits throughput: 1.100 ± 0.047 M ops/s > local_storage cache interleaved get: hits throughput: 131.979 ± 5.013 M ops/s, hits latency: 7.577 ns/op, important_hits throughput: 34.472 ± 1.309 M ops/s > > num_maps: 1000 > local_storage cache sequential get: hits throughput: 117.850 ± 2.423 M ops/s, hits latency: 8.485 ns/op, important_hits throughput: 0.118 ± 0.002 M ops/s > local_storage cache interleaved get: hits throughput: 141.268 ± 9.658 M ops/s, hits latency: 7.079 ns/op, important_hits throughput: 35.476 ± 2.425 M ops/s > > Adjusting for overhead, latency numbers for "hashmap control" and "sequential get" are: > > hashmap_control: ~10.4ns > sequential_get_1: ~13.0ns So what this benchmark doesn't demonstrate is why one would use local storage at all if hashmap is so fast :) I think at least partially it's because of your choice to do fixed hashmap lookup with zero key. Think about how you'd replace local_storage with hashmap. You'd have task/socket/whatever ID as look up key. For different tasks you'd be looking up different pids. For your benchmark you have the same task all the time, but local_storage look up still does all the work to find local storage instance in a list of local storages for current task, so you don't have to use many tasks to simulate realistic lookup overhead (well, at least to some extent). But it seems not realistic for testing hashmap as an alternative to local_storage, for that I think we'd need to randomize key look up a bit. Unless I misunderstand what we are testing for hashmap use case. But other than that LGTM. > sequential_get_10: ~13.8ns > sequential_get_16: ~13.6ns > sequential_get_17: ~21.5ns > sequential_get_24: ~42.5ns > sequential_get_32: ~65.9ns > sequential_get_100: ~155.7ns > sequential_get_1000: ~2270ns > > Clearly demonstrating a cliff. > > When running the benchmarks it may be necessary to bump 'open files' > ulimit for a successful run. > > [0]: https://lore.kernel.org/all/20220420002143.1096548-1-davemarchevsky@fb.com > > Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> > --- > Changelog: > > v3 -> v4: > * Remove ifs guarding increments in measure fn (Andrii) > * Refactor to use 1 bpf prog for all 3 benchmarks w/ global vars set > from userspace before load to control behavior (Andrii) > * Greatly reduce variance in overhead by having benchmark bpf prog > loop 10k times regardless of map count (Andrii) > * Also, move sync_fetch_and_incr out of do_lookup as the guaranteed > second sync_fetch_and_incr call for num_maps = 1 was adding > overhead > * Add second patch refactoring bench.c's mean/stddev calculations > in reporting helper fns > > v2 -> v3: > * Accessing 1k maps in ARRAY_OF_MAPS doesn't hit MAX_USED_MAPS limit, > so just use 1 program (Alexei) > > v1 -> v2: > * Adopt ARRAY_OF_MAPS approach for bpf program, allowing truly > configurable # of maps (Andrii) > * Add hashmap benchmark (Alexei) > * Add discussion of overhead > > tools/testing/selftests/bpf/Makefile | 4 +- > tools/testing/selftests/bpf/bench.c | 55 ++++ > tools/testing/selftests/bpf/bench.h | 4 + > .../bpf/benchs/bench_local_storage.c | 250 ++++++++++++++++++ > .../bpf/benchs/run_bench_local_storage.sh | 21 ++ > .../selftests/bpf/benchs/run_common.sh | 17 ++ > .../selftests/bpf/progs/local_storage_bench.c | 99 +++++++ > 7 files changed, 449 insertions(+), 1 deletion(-) > create mode 100644 tools/testing/selftests/bpf/benchs/bench_local_storage.c > create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh > create mode 100644 tools/testing/selftests/bpf/progs/local_storage_bench.c > [...] > + > +static void hashmap_setup(void) > +{ > + struct local_storage_bench *skel; > + > + setup_libbpf(); > + > + skel = local_storage_bench__open(); > + ctx.skel = skel; > + ctx.bpf_obj = skel->obj; nit: ctx.skel->obj is the same as ctx.bpf_obj, so bpf_obj is probably not needed? > + ctx.array_of_maps = skel->maps.array_of_hash_maps; > + skel->rodata->use_hashmap = 1; > + skel->rodata->interleave = 0; > + > + __setup(skel->progs.get_local, true); > +} > + [...]
On 6/3/22 5:26 PM, Andrii Nakryiko wrote: > On Mon, May 30, 2022 at 1:27 PM Dave Marchevsky <davemarchevsky@fb.com> wrote: >> >> Add a benchmarks to demonstrate the performance cliff for local_storage >> get as the number of local_storage maps increases beyond current >> local_storage implementation's cache size. >> >> "sequential get" and "interleaved get" benchmarks are added, both of >> which do many bpf_task_storage_get calls on sets of task local_storage >> maps of various counts, while considering a single specific map to be >> 'important' and counting task_storage_gets to the important map >> separately in addition to normal 'hits' count of all gets. Goal here is >> to mimic scenario where a particular program using one map - the >> important one - is running on a system where many other local_storage >> maps exist and are accessed often. >> >> While "sequential get" benchmark does bpf_task_storage_get for map 0, 1, >> ..., {9, 99, 999} in order, "interleaved" benchmark interleaves 4 >> bpf_task_storage_gets for the important map for every 10 map gets. This >> is meant to highlight performance differences when important map is >> accessed far more frequently than non-important maps. >> >> A "hashmap control" benchmark is also included for easy comparison of >> standard bpf hashmap lookup vs local_storage get. The benchmark is >> identical to "sequential get", but creates and uses BPF_MAP_TYPE_HASH >> instead of local storage. >> >> Addition of this benchmark is inspired by conversation with Alexei in a >> previous patchset's thread [0], which highlighted the need for such a >> benchmark to motivate and validate improvements to local_storage >> implementation. My approach in that series focused on improving >> performance for explicitly-marked 'important' maps and was rejected >> with feedback to make more generally-applicable improvements while >> avoiding explicitly marking maps as important. Thus the benchmark >> reports both general and important-map-focused metrics, so effect of >> future work on both is clear. >> >> Regarding the benchmark results. On a powerful system (Skylake, 20 >> cores, 256gb ram): >> >> Local Storage >> ============= >> Hashmap Control w/ 500 maps >> hashmap (control) sequential get: hits throughput: 48.338 ± 2.366 M ops/s, hits latency: 20.688 ns/op, important_hits throughput: 0.097 ± 0.005 M ops/s >> >> num_maps: 1 >> local_storage cache sequential get: hits throughput: 44.503 ± 1.080 M ops/s, hits latency: 22.470 ns/op, important_hits throughput: 44.503 ± 1.080 M ops/s >> local_storage cache interleaved get: hits throughput: 54.963 ± 0.586 M ops/s, hits latency: 18.194 ns/op, important_hits throughput: 54.963 ± 0.586 M ops/s >> >> num_maps: 10 >> local_storage cache sequential get: hits throughput: 43.743 ± 0.418 M ops/s, hits latency: 22.861 ns/op, important_hits throughput: 4.374 ± 0.042 M ops/s >> local_storage cache interleaved get: hits throughput: 50.073 ± 0.609 M ops/s, hits latency: 19.971 ns/op, important_hits throughput: 17.883 ± 0.217 M ops/s >> >> num_maps: 16 >> local_storage cache sequential get: hits throughput: 43.962 ± 0.525 M ops/s, hits latency: 22.747 ns/op, important_hits throughput: 2.748 ± 0.033 M ops/s >> local_storage cache interleaved get: hits throughput: 48.166 ± 0.825 M ops/s, hits latency: 20.761 ns/op, important_hits throughput: 15.326 ± 0.263 M ops/s >> >> num_maps: 17 >> local_storage cache sequential get: hits throughput: 33.207 ± 0.461 M ops/s, hits latency: 30.114 ns/op, important_hits throughput: 1.956 ± 0.027 M ops/s >> local_storage cache interleaved get: hits throughput: 43.540 ± 0.265 M ops/s, hits latency: 22.968 ns/op, important_hits throughput: 13.255 ± 0.081 M ops/s >> >> num_maps: 24 >> local_storage cache sequential get: hits throughput: 19.402 ± 0.348 M ops/s, hits latency: 51.542 ns/op, important_hits throughput: 0.809 ± 0.015 M ops/s >> local_storage cache interleaved get: hits throughput: 22.981 ± 0.487 M ops/s, hits latency: 43.514 ns/op, important_hits throughput: 6.465 ± 0.137 M ops/s >> >> num_maps: 32 >> local_storage cache sequential get: hits throughput: 13.378 ± 0.220 M ops/s, hits latency: 74.748 ns/op, important_hits throughput: 0.419 ± 0.007 M ops/s >> local_storage cache interleaved get: hits throughput: 16.894 ± 0.172 M ops/s, hits latency: 59.193 ns/op, important_hits throughput: 4.716 ± 0.048 M ops/s >> >> num_maps: 100 >> local_storage cache sequential get: hits throughput: 6.070 ± 0.140 M ops/s, hits latency: 164.745 ns/op, important_hits throughput: 0.061 ± 0.001 M ops/s >> local_storage cache interleaved get: hits throughput: 7.323 ± 0.149 M ops/s, hits latency: 136.554 ns/op, important_hits throughput: 1.913 ± 0.039 M ops/s >> >> num_maps: 1000 >> local_storage cache sequential get: hits throughput: 0.438 ± 0.012 M ops/s, hits latency: 2281.369 ns/op, important_hits throughput: 0.000 ± 0.000 M ops/s >> local_storage cache interleaved get: hits throughput: 0.522 ± 0.010 M ops/s, hits latency: 1913.937 ns/op, important_hits throughput: 0.131 ± 0.003 M ops/s >> >> Looking at the "sequential get" results, it's clear that as the >> number of task local_storage maps grows beyond the current cache size >> (16), there's a significant reduction in hits throughput. Note that >> current local_storage implementation assigns a cache_idx to maps as they >> are created. Since "sequential get" is creating maps 0..n in order and >> then doing bpf_task_storage_get calls in the same order, the benchmark >> is effectively ensuring that a map will not be in cache when the program >> tries to access it. >> >> For "interleaved get" results, important-map hits throughput is greatly >> increased as the important map is more likely to be in cache by virtue >> of being accessed far more frequently. Throughput still reduces as # >> maps increases, though. >> >> To get a sense of the overhead of the benchmark program, I >> commented out bpf_task_storage_get/bpf_map_lookup_elem in >> local_storage_bench.c and ran the benchmark on the same host as the >> 'real' run. Results: >> >> Local Storage >> ============= >> Hashmap Control w/ 500 maps >> hashmap (control) sequential get: hits throughput: 96.965 ± 1.346 M ops/s, hits latency: 10.313 ns/op, important_hits throughput: 0.194 ± 0.003 M ops/s >> >> num_maps: 1 >> local_storage cache sequential get: hits throughput: 105.792 ± 1.860 M ops/s, hits latency: 9.453 ns/op, important_hits throughput: 105.792 ± 1.860 M ops/s >> local_storage cache interleaved get: hits throughput: 185.847 ± 4.014 M ops/s, hits latency: 5.381 ns/op, important_hits throughput: 185.847 ± 4.014 M ops/s >> >> num_maps: 10 >> local_storage cache sequential get: hits throughput: 109.867 ± 1.358 M ops/s, hits latency: 9.102 ns/op, important_hits throughput: 10.987 ± 0.136 M ops/s >> local_storage cache interleaved get: hits throughput: 144.165 ± 1.256 M ops/s, hits latency: 6.936 ns/op, important_hits throughput: 51.487 ± 0.449 M ops/s >> >> num_maps: 16 >> local_storage cache sequential get: hits throughput: 109.258 ± 1.902 M ops/s, hits latency: 9.153 ns/op, important_hits throughput: 6.829 ± 0.119 M ops/s >> local_storage cache interleaved get: hits throughput: 140.248 ± 1.836 M ops/s, hits latency: 7.130 ns/op, important_hits throughput: 44.624 ± 0.584 M ops/s >> >> num_maps: 17 >> local_storage cache sequential get: hits throughput: 116.397 ± 7.679 M ops/s, hits latency: 8.591 ns/op, important_hits throughput: 6.856 ± 0.452 M ops/s >> local_storage cache interleaved get: hits throughput: 128.411 ± 4.927 M ops/s, hits latency: 7.787 ns/op, important_hits throughput: 39.093 ± 1.500 M ops/s >> >> num_maps: 24 >> local_storage cache sequential get: hits throughput: 110.890 ± 0.976 M ops/s, hits latency: 9.018 ns/op, important_hits throughput: 4.624 ± 0.041 M ops/s >> local_storage cache interleaved get: hits throughput: 133.316 ± 1.889 M ops/s, hits latency: 7.501 ns/op, important_hits throughput: 37.503 ± 0.531 M ops/s >> >> num_maps: 32 >> local_storage cache sequential get: hits throughput: 112.900 ± 1.171 M ops/s, hits latency: 8.857 ns/op, important_hits throughput: 3.534 ± 0.037 M ops/s >> local_storage cache interleaved get: hits throughput: 132.844 ± 1.207 M ops/s, hits latency: 7.528 ns/op, important_hits throughput: 37.081 ± 0.337 M ops/s >> >> num_maps: 100 >> local_storage cache sequential get: hits throughput: 110.025 ± 4.714 M ops/s, hits latency: 9.089 ns/op, important_hits throughput: 1.100 ± 0.047 M ops/s >> local_storage cache interleaved get: hits throughput: 131.979 ± 5.013 M ops/s, hits latency: 7.577 ns/op, important_hits throughput: 34.472 ± 1.309 M ops/s >> >> num_maps: 1000 >> local_storage cache sequential get: hits throughput: 117.850 ± 2.423 M ops/s, hits latency: 8.485 ns/op, important_hits throughput: 0.118 ± 0.002 M ops/s >> local_storage cache interleaved get: hits throughput: 141.268 ± 9.658 M ops/s, hits latency: 7.079 ns/op, important_hits throughput: 35.476 ± 2.425 M ops/s >> >> Adjusting for overhead, latency numbers for "hashmap control" and "sequential get" are: >> >> hashmap_control: ~10.4ns >> sequential_get_1: ~13.0ns > > So what this benchmark doesn't demonstrate is why one would use local > storage at all if hashmap is so fast :) > > I think at least partially it's because of your choice to do fixed > hashmap lookup with zero key. Think about how you'd replace > local_storage with hashmap. You'd have task/socket/whatever ID as look > up key. For different tasks you'd be looking up different pids. For > your benchmark you have the same task all the time, but local_storage > look up still does all the work to find local storage instance in a > list of local storages for current task, so you don't have to use many > tasks to simulate realistic lookup overhead (well, at least to some > extent). But it seems not realistic for testing hashmap as an > alternative to local_storage, for that I think we'd need to randomize > key look up a bit. Unless I misunderstand what we are testing for > hashmap use case. > > But other than that LGTM. This makes more sense than what I'm doing now, and I think better fulfills Alexei's request from v1 of this series: Also could you add a hash map with key=tid. It would be interesting to compare local storage with hash map. iirc when local storage was introduced it was 2.5 times faster than large hashmap. Since then both have changed. I tried changing the "hashmap control" benchmark to just have 1 inner hashmap, with max_entries 4,194,304 (PID_MAX_LIMIT on my system). use_hashmap branch of bpf prog does bpf_get_prandom_u32 to select key. Results are more promising: Overhead: ~19.5ns (prandom call + additional modulo) 4,194,304 possible keys: ~150.5ns (~131ns w/o overhead) 100,000 possible keys: ~55ns (~35.5ns w/o overhead) 1,000 possible keys: ~31ns (~11.5ns w/o overhead) 10 possible keys: ~28ns (~8.5ns w/o overhead) So big hashmap with only a few keys used is faster than local_storage but far slower when many keys used. Somewhere between "100k keys" and "1k keys" is probably what performance would look like if a program which needed an entry per running task used hashmap instead of local_storage. Close to Alexei's memory of 2.5x difference. Will send in v5. > >> sequential_get_10: ~13.8ns >> sequential_get_16: ~13.6ns >> sequential_get_17: ~21.5ns >> sequential_get_24: ~42.5ns >> sequential_get_32: ~65.9ns >> sequential_get_100: ~155.7ns >> sequential_get_1000: ~2270ns >> >> Clearly demonstrating a cliff. >> >> When running the benchmarks it may be necessary to bump 'open files' >> ulimit for a successful run. >> >> [0]: https://lore.kernel.org/all/20220420002143.1096548-1-davemarchevsky@fb.com >> >> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> >> --- >> Changelog: >> >> v3 -> v4: >> * Remove ifs guarding increments in measure fn (Andrii) >> * Refactor to use 1 bpf prog for all 3 benchmarks w/ global vars set >> from userspace before load to control behavior (Andrii) >> * Greatly reduce variance in overhead by having benchmark bpf prog >> loop 10k times regardless of map count (Andrii) >> * Also, move sync_fetch_and_incr out of do_lookup as the guaranteed >> second sync_fetch_and_incr call for num_maps = 1 was adding >> overhead >> * Add second patch refactoring bench.c's mean/stddev calculations >> in reporting helper fns >> >> v2 -> v3: >> * Accessing 1k maps in ARRAY_OF_MAPS doesn't hit MAX_USED_MAPS limit, >> so just use 1 program (Alexei) >> >> v1 -> v2: >> * Adopt ARRAY_OF_MAPS approach for bpf program, allowing truly >> configurable # of maps (Andrii) >> * Add hashmap benchmark (Alexei) >> * Add discussion of overhead >> >> tools/testing/selftests/bpf/Makefile | 4 +- >> tools/testing/selftests/bpf/bench.c | 55 ++++ >> tools/testing/selftests/bpf/bench.h | 4 + >> .../bpf/benchs/bench_local_storage.c | 250 ++++++++++++++++++ >> .../bpf/benchs/run_bench_local_storage.sh | 21 ++ >> .../selftests/bpf/benchs/run_common.sh | 17 ++ >> .../selftests/bpf/progs/local_storage_bench.c | 99 +++++++ >> 7 files changed, 449 insertions(+), 1 deletion(-) >> create mode 100644 tools/testing/selftests/bpf/benchs/bench_local_storage.c >> create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh >> create mode 100644 tools/testing/selftests/bpf/progs/local_storage_bench.c >> > > [...] > >> + >> +static void hashmap_setup(void) >> +{ >> + struct local_storage_bench *skel; >> + >> + setup_libbpf(); >> + >> + skel = local_storage_bench__open(); >> + ctx.skel = skel; >> + ctx.bpf_obj = skel->obj; > > nit: ctx.skel->obj is the same as ctx.bpf_obj, so bpf_obj is probably > not needed? Will get rid of it in v5. > > >> + ctx.array_of_maps = skel->maps.array_of_hash_maps; >> + skel->rodata->use_hashmap = 1; >> + skel->rodata->interleave = 0; >> + >> + __setup(skel->progs.get_local, true); >> +} >> + > > [...]
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 2d3c8c8f558a..f82f77075f67 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -560,6 +560,7 @@ $(OUTPUT)/bench_ringbufs.o: $(OUTPUT)/ringbuf_bench.skel.h \ $(OUTPUT)/bench_bloom_filter_map.o: $(OUTPUT)/bloom_filter_bench.skel.h $(OUTPUT)/bench_bpf_loop.o: $(OUTPUT)/bpf_loop_bench.skel.h $(OUTPUT)/bench_strncmp.o: $(OUTPUT)/strncmp_bench.skel.h +$(OUTPUT)/bench_local_storage.o: $(OUTPUT)/local_storage_bench.skel.h $(OUTPUT)/bench.o: bench.h testing_helpers.h $(BPFOBJ) $(OUTPUT)/bench: LDLIBS += -lm $(OUTPUT)/bench: $(OUTPUT)/bench.o \ @@ -571,7 +572,8 @@ $(OUTPUT)/bench: $(OUTPUT)/bench.o \ $(OUTPUT)/bench_ringbufs.o \ $(OUTPUT)/bench_bloom_filter_map.o \ $(OUTPUT)/bench_bpf_loop.o \ - $(OUTPUT)/bench_strncmp.o + $(OUTPUT)/bench_strncmp.o \ + $(OUTPUT)/bench_local_storage.o $(call msg,BINARY,,$@) $(Q)$(CC) $(CFLAGS) $(LDFLAGS) $(filter %.a %.o,$^) $(LDLIBS) -o $@ diff --git a/tools/testing/selftests/bpf/bench.c b/tools/testing/selftests/bpf/bench.c index f061cc20e776..32399554f89b 100644 --- a/tools/testing/selftests/bpf/bench.c +++ b/tools/testing/selftests/bpf/bench.c @@ -150,6 +150,53 @@ void ops_report_final(struct bench_res res[], int res_cnt) printf("latency %8.3lf ns/op\n", 1000.0 / hits_mean * env.producer_cnt); } +void local_storage_report_progress(int iter, struct bench_res *res, + long delta_ns) +{ + double important_hits_per_sec, hits_per_sec; + double delta_sec = delta_ns / 1000000000.0; + + hits_per_sec = res->hits / 1000000.0 / delta_sec; + important_hits_per_sec = res->important_hits / 1000000.0 / delta_sec; + + printf("Iter %3d (%7.3lfus): ", iter, (delta_ns - 1000000000) / 1000.0); + + printf("hits %8.3lfM/s ", hits_per_sec); + printf("important_hits %8.3lfM/s\n", important_hits_per_sec); +} + +void local_storage_report_final(struct bench_res res[], int res_cnt) +{ + double important_hits_mean = 0.0, important_hits_stddev = 0.0; + double hits_mean = 0.0, hits_stddev = 0.0; + int i; + + for (i = 0; i < res_cnt; i++) { + hits_mean += res[i].hits / 1000000.0 / (0.0 + res_cnt); + important_hits_mean += res[i].important_hits / 1000000.0 / (0.0 + res_cnt); + } + + if (res_cnt > 1) { + for (i = 0; i < res_cnt; i++) { + hits_stddev += (hits_mean - res[i].hits / 1000000.0) * + (hits_mean - res[i].hits / 1000000.0) / + (res_cnt - 1.0); + important_hits_stddev += + (important_hits_mean - res[i].important_hits / 1000000.0) * + (important_hits_mean - res[i].important_hits / 1000000.0) / + (res_cnt - 1.0); + } + + hits_stddev = sqrt(hits_stddev); + important_hits_stddev = sqrt(important_hits_stddev); + } + printf("Summary: hits throughput %8.3lf \u00B1 %5.3lf M ops/s, ", + hits_mean, hits_stddev); + printf("hits latency %8.3lf ns/op, ", 1000.0 / hits_mean); + printf("important_hits throughput %8.3lf \u00B1 %5.3lf M ops/s\n", + important_hits_mean, important_hits_stddev); +} + const char *argp_program_version = "benchmark"; const char *argp_program_bug_address = "<bpf@vger.kernel.org>"; const char argp_program_doc[] = @@ -188,12 +235,14 @@ static const struct argp_option opts[] = { extern struct argp bench_ringbufs_argp; extern struct argp bench_bloom_map_argp; extern struct argp bench_bpf_loop_argp; +extern struct argp bench_local_storage_argp; extern struct argp bench_strncmp_argp; static const struct argp_child bench_parsers[] = { { &bench_ringbufs_argp, 0, "Ring buffers benchmark", 0 }, { &bench_bloom_map_argp, 0, "Bloom filter map benchmark", 0 }, { &bench_bpf_loop_argp, 0, "bpf_loop helper benchmark", 0 }, + { &bench_local_storage_argp, 0, "local_storage benchmark", 0 }, { &bench_strncmp_argp, 0, "bpf_strncmp helper benchmark", 0 }, {}, }; @@ -396,6 +445,9 @@ extern const struct bench bench_hashmap_with_bloom; extern const struct bench bench_bpf_loop; extern const struct bench bench_strncmp_no_helper; extern const struct bench bench_strncmp_helper; +extern const struct bench bench_local_storage_cache_seq_get; +extern const struct bench bench_local_storage_cache_interleaved_get; +extern const struct bench bench_local_storage_cache_hashmap_control; static const struct bench *benchs[] = { &bench_count_global, @@ -430,6 +482,9 @@ static const struct bench *benchs[] = { &bench_bpf_loop, &bench_strncmp_no_helper, &bench_strncmp_helper, + &bench_local_storage_cache_seq_get, + &bench_local_storage_cache_interleaved_get, + &bench_local_storage_cache_hashmap_control, }; static void setup_benchmark() diff --git a/tools/testing/selftests/bpf/bench.h b/tools/testing/selftests/bpf/bench.h index fb3e213df3dc..4b15286753ba 100644 --- a/tools/testing/selftests/bpf/bench.h +++ b/tools/testing/selftests/bpf/bench.h @@ -34,6 +34,7 @@ struct bench_res { long hits; long drops; long false_hits; + long important_hits; }; struct bench { @@ -61,6 +62,9 @@ void false_hits_report_progress(int iter, struct bench_res *res, long delta_ns); void false_hits_report_final(struct bench_res res[], int res_cnt); void ops_report_progress(int iter, struct bench_res *res, long delta_ns); void ops_report_final(struct bench_res res[], int res_cnt); +void local_storage_report_progress(int iter, struct bench_res *res, + long delta_ns); +void local_storage_report_final(struct bench_res res[], int res_cnt); static inline __u64 get_time_ns(void) { diff --git a/tools/testing/selftests/bpf/benchs/bench_local_storage.c b/tools/testing/selftests/bpf/benchs/bench_local_storage.c new file mode 100644 index 000000000000..93e68b589625 --- /dev/null +++ b/tools/testing/selftests/bpf/benchs/bench_local_storage.c @@ -0,0 +1,250 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */ + +#include <argp.h> +#include <linux/btf.h> + +#include "local_storage_bench.skel.h" +#include "bench.h" + +#include <test_btf.h> + +static struct { + __u32 nr_maps; +} args = { + .nr_maps = 100, +}; + +enum { + ARG_NR_MAPS = 6000, +}; + +static const struct argp_option opts[] = { + { "nr_maps", ARG_NR_MAPS, "NR_MAPS", 0, + "Set number of local_storage maps"}, + {}, +}; + +static error_t parse_arg(int key, char *arg, struct argp_state *state) +{ + long ret; + + switch (key) { + case ARG_NR_MAPS: + ret = strtol(arg, NULL, 10); + if (ret < 1 || ret > UINT_MAX) { + fprintf(stderr, "invalid nr_maps"); + argp_usage(state); + } + args.nr_maps = ret; + break; + default: + return ARGP_ERR_UNKNOWN; + } + + return 0; +} + +const struct argp bench_local_storage_argp = { + .options = opts, + .parser = parse_arg, +}; + +/* Keep in sync w/ array of maps in bpf */ +#define MAX_NR_MAPS 1000 + +static void validate(void) +{ + if (env.producer_cnt != 1) { + fprintf(stderr, "benchmark doesn't support multi-producer!\n"); + exit(1); + } + if (env.consumer_cnt != 1) { + fprintf(stderr, "benchmark doesn't support multi-consumer!\n"); + exit(1); + } + + if (args.nr_maps > MAX_NR_MAPS) { + fprintf(stderr, "nr_maps must be <= 1000\n"); + exit(1); + } +} + +static struct { + struct local_storage_bench *skel; + void *bpf_obj; + struct bpf_map *array_of_maps; +} ctx; + +static void __setup(struct bpf_program *prog, bool hashmap) +{ + struct bpf_map *inner_map; + int i, fd, mim_fd, err; + + LIBBPF_OPTS(bpf_map_create_opts, create_opts); + + if (!hashmap) + create_opts.map_flags = BPF_F_NO_PREALLOC; + + ctx.skel->rodata->num_maps = args.nr_maps; + inner_map = bpf_map__inner_map(ctx.array_of_maps); + create_opts.btf_key_type_id = bpf_map__btf_key_type_id(inner_map); + create_opts.btf_value_type_id = bpf_map__btf_value_type_id(inner_map); + + err = local_storage_bench__load(ctx.skel); + if (err) { + fprintf(stderr, "Error loading skeleton\n"); + goto err_out; + } + + create_opts.btf_fd = bpf_object__btf_fd(ctx.bpf_obj); + + mim_fd = bpf_map__fd(ctx.array_of_maps); + if (mim_fd < 0) { + fprintf(stderr, "Error getting map_in_map fd\n"); + goto err_out; + } + + for (i = 0; i < args.nr_maps; i++) { + if (hashmap) + fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(int), + sizeof(int), 65536, &create_opts); + else + fd = bpf_map_create(BPF_MAP_TYPE_TASK_STORAGE, NULL, sizeof(int), + sizeof(int), 0, &create_opts); + if (fd < 0) { + fprintf(stderr, "Error creating map %d: %d\n", i, fd); + goto err_out; + } + + err = bpf_map_update_elem(mim_fd, &i, &fd, 0); + if (err) { + fprintf(stderr, "Error updating array-of-maps w/ map %d\n", i); + goto err_out; + } + } + + if (!bpf_program__attach(prog)) { + fprintf(stderr, "Error attaching bpf program\n"); + goto err_out; + } + + return; +err_out: + exit(1); +} + +static void hashmap_setup(void) +{ + struct local_storage_bench *skel; + + setup_libbpf(); + + skel = local_storage_bench__open(); + ctx.skel = skel; + ctx.bpf_obj = skel->obj; + ctx.array_of_maps = skel->maps.array_of_hash_maps; + skel->rodata->use_hashmap = 1; + skel->rodata->interleave = 0; + + __setup(skel->progs.get_local, true); +} + +static void local_storage_cache_get_setup(void) +{ + struct local_storage_bench *skel; + + setup_libbpf(); + + skel = local_storage_bench__open(); + ctx.skel = skel; + ctx.bpf_obj = skel->obj; + ctx.array_of_maps = skel->maps.array_of_local_storage_maps; + skel->rodata->use_hashmap = 0; + skel->rodata->interleave = 0; + + __setup(skel->progs.get_local, false); +} + +static void local_storage_cache_get_interleaved_setup(void) +{ + struct local_storage_bench *skel; + + setup_libbpf(); + + skel = local_storage_bench__open(); + ctx.skel = skel; + ctx.bpf_obj = skel->obj; + ctx.array_of_maps = skel->maps.array_of_local_storage_maps; + skel->rodata->use_hashmap = 0; + skel->rodata->interleave = 1; + + __setup(skel->progs.get_local, false); +} + +static void measure(struct bench_res *res) +{ + res->hits = atomic_swap(&ctx.skel->bss->hits, 0); + res->important_hits = atomic_swap(&ctx.skel->bss->important_hits, 0); +} + +static inline void trigger_bpf_program(void) +{ + syscall(__NR_getpgid); +} + +static void *consumer(void *input) +{ + return NULL; +} + +static void *producer(void *input) +{ + while (true) + trigger_bpf_program(); + + return NULL; +} + +/* cache sequential and interleaved get benchs test local_storage get + * performance, specifically they demonstrate performance cliff of + * current list-plus-cache local_storage model. + * + * cache sequential get: call bpf_task_storage_get on n maps in order + * cache interleaved get: like "sequential get", but interleave 4 calls to the + * 'important' map (idx 0 in array_of_maps) for every 10 calls. Goal + * is to mimic environment where many progs are accessing their local_storage + * maps, with 'our' prog needing to access its map more often than others + */ +const struct bench bench_local_storage_cache_seq_get = { + .name = "local-storage-cache-seq-get", + .validate = validate, + .setup = local_storage_cache_get_setup, + .producer_thread = producer, + .consumer_thread = consumer, + .measure = measure, + .report_progress = local_storage_report_progress, + .report_final = local_storage_report_final, +}; + +const struct bench bench_local_storage_cache_interleaved_get = { + .name = "local-storage-cache-int-get", + .validate = validate, + .setup = local_storage_cache_get_interleaved_setup, + .producer_thread = producer, + .consumer_thread = consumer, + .measure = measure, + .report_progress = local_storage_report_progress, + .report_final = local_storage_report_final, +}; + +const struct bench bench_local_storage_cache_hashmap_control = { + .name = "local-storage-cache-hashmap-control", + .validate = validate, + .setup = hashmap_setup, + .producer_thread = producer, + .consumer_thread = consumer, + .measure = measure, + .report_progress = local_storage_report_progress, + .report_final = local_storage_report_final, +}; diff --git a/tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh b/tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh new file mode 100755 index 000000000000..479096c47c93 --- /dev/null +++ b/tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh @@ -0,0 +1,21 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 + +source ./benchs/run_common.sh + +set -eufo pipefail + +header "Local Storage" +subtitle "Hashmap Control w/ 500 maps" + summarize_local_storage "hashmap (control) sequential get: "\ + "$(./bench --nr_maps 500 local-storage-cache-hashmap-control)" + printf "\n" + +for i in 1 10 16 17 24 32 100 1000; do +subtitle "num_maps: $i" + summarize_local_storage "local_storage cache sequential get: "\ + "$(./bench --nr_maps $i local-storage-cache-seq-get)" + summarize_local_storage "local_storage cache interleaved get: "\ + "$(./bench --nr_maps $i local-storage-cache-int-get)" + printf "\n" +done diff --git a/tools/testing/selftests/bpf/benchs/run_common.sh b/tools/testing/selftests/bpf/benchs/run_common.sh index 6c5e6023a69f..d9f40af82006 100644 --- a/tools/testing/selftests/bpf/benchs/run_common.sh +++ b/tools/testing/selftests/bpf/benchs/run_common.sh @@ -41,6 +41,16 @@ function ops() echo "$*" | sed -E "s/.*latency\s+([0-9]+\.[0-9]+\sns\/op).*/\1/" } +function local_storage() +{ + echo -n "hits throughput: " + echo -n "$*" | sed -E "s/.* hits throughput\s+([0-9]+\.[0-9]+ ± [0-9]+\.[0-9]+\sM\sops\/s).*/\1/" + echo -n -e ", hits latency: " + echo -n "$*" | sed -E "s/.* hits latency\s+([0-9]+\.[0-9]+\sns\/op).*/\1/" + echo -n ", important_hits throughput: " + echo "$*" | sed -E "s/.*important_hits throughput\s+([0-9]+\.[0-9]+ ± [0-9]+\.[0-9]+\sM\sops\/s).*/\1/" +} + function total() { echo "$*" | sed -E "s/.*total operations\s+([0-9]+\.[0-9]+ ± [0-9]+\.[0-9]+M\/s).*/\1/" @@ -67,6 +77,13 @@ function summarize_ops() printf "%-20s %s\n" "$bench" "$(ops $summary)" } +function summarize_local_storage() +{ + bench="$1" + summary=$(echo $2 | tail -n1) + printf "%-20s %s\n" "$bench" "$(local_storage $summary)" +} + function summarize_total() { bench="$1" diff --git a/tools/testing/selftests/bpf/progs/local_storage_bench.c b/tools/testing/selftests/bpf/progs/local_storage_bench.c new file mode 100644 index 000000000000..68a6e88e5d7c --- /dev/null +++ b/tools/testing/selftests/bpf/progs/local_storage_bench.c @@ -0,0 +1,99 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */ + +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include "bpf_misc.h" + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS); + __uint(max_entries, 1000); + __type(key, int); + __type(value, int); + __array(values, struct { + __uint(type, BPF_MAP_TYPE_TASK_STORAGE); + __uint(map_flags, BPF_F_NO_PREALLOC); + __type(key, int); + __type(value, int); + }); +} array_of_local_storage_maps SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS); + __uint(max_entries, 1000); + __type(key, int); + __type(value, int); + __array(values, struct { + __uint(type, BPF_MAP_TYPE_HASH); + __uint(max_entries, 65536); + __type(key, int); + __type(value, int); + }); +} array_of_hash_maps SEC(".maps"); + +long important_hits; +long hits; + +/* set from user-space */ +const volatile unsigned int use_hashmap; +const volatile unsigned int num_maps; +const volatile unsigned int interleave; + +struct loop_ctx { + struct task_struct *task; + long loop_hits; + long loop_important_hits; +}; + +static int do_lookup(unsigned int elem, struct loop_ctx *lctx) +{ + void *map, *inner_map; + int zero = 0; + + if (use_hashmap) + map = &array_of_hash_maps; + else + map = &array_of_local_storage_maps; + + inner_map = bpf_map_lookup_elem(map, &elem); + if (!inner_map) + return -1; + + if (use_hashmap) + bpf_map_lookup_elem(inner_map, &zero); + else + bpf_task_storage_get(inner_map, lctx->task, &zero, + BPF_LOCAL_STORAGE_GET_F_CREATE); + + lctx->loop_hits++; + if (!elem) + lctx->loop_important_hits++; + return 0; +} + +static long loop(u32 index, void *ctx) +{ + struct loop_ctx *lctx = (struct loop_ctx *)ctx; + unsigned int map_idx = index % num_maps; + + do_lookup(map_idx, lctx); + if (interleave && map_idx % 3 == 0) + do_lookup(0, lctx); + return 0; +} + +SEC("fentry/" SYS_PREFIX "sys_getpgid") +int get_local(void *ctx) +{ + struct loop_ctx lctx; + + lctx.task = bpf_get_current_task_btf(); + lctx.loop_hits = 0; + lctx.loop_important_hits = 0; + bpf_loop(10000, &loop, &lctx, 0); + __sync_add_and_fetch(&hits, lctx.loop_hits); + __sync_add_and_fetch(&important_hits, lctx.loop_important_hits); + return 0; +} + +char _license[] SEC("license") = "GPL";
Add a benchmarks to demonstrate the performance cliff for local_storage get as the number of local_storage maps increases beyond current local_storage implementation's cache size. "sequential get" and "interleaved get" benchmarks are added, both of which do many bpf_task_storage_get calls on sets of task local_storage maps of various counts, while considering a single specific map to be 'important' and counting task_storage_gets to the important map separately in addition to normal 'hits' count of all gets. Goal here is to mimic scenario where a particular program using one map - the important one - is running on a system where many other local_storage maps exist and are accessed often. While "sequential get" benchmark does bpf_task_storage_get for map 0, 1, ..., {9, 99, 999} in order, "interleaved" benchmark interleaves 4 bpf_task_storage_gets for the important map for every 10 map gets. This is meant to highlight performance differences when important map is accessed far more frequently than non-important maps. A "hashmap control" benchmark is also included for easy comparison of standard bpf hashmap lookup vs local_storage get. The benchmark is identical to "sequential get", but creates and uses BPF_MAP_TYPE_HASH instead of local storage. Addition of this benchmark is inspired by conversation with Alexei in a previous patchset's thread [0], which highlighted the need for such a benchmark to motivate and validate improvements to local_storage implementation. My approach in that series focused on improving performance for explicitly-marked 'important' maps and was rejected with feedback to make more generally-applicable improvements while avoiding explicitly marking maps as important. Thus the benchmark reports both general and important-map-focused metrics, so effect of future work on both is clear. Regarding the benchmark results. On a powerful system (Skylake, 20 cores, 256gb ram): Local Storage ============= Hashmap Control w/ 500 maps hashmap (control) sequential get: hits throughput: 48.338 ± 2.366 M ops/s, hits latency: 20.688 ns/op, important_hits throughput: 0.097 ± 0.005 M ops/s num_maps: 1 local_storage cache sequential get: hits throughput: 44.503 ± 1.080 M ops/s, hits latency: 22.470 ns/op, important_hits throughput: 44.503 ± 1.080 M ops/s local_storage cache interleaved get: hits throughput: 54.963 ± 0.586 M ops/s, hits latency: 18.194 ns/op, important_hits throughput: 54.963 ± 0.586 M ops/s num_maps: 10 local_storage cache sequential get: hits throughput: 43.743 ± 0.418 M ops/s, hits latency: 22.861 ns/op, important_hits throughput: 4.374 ± 0.042 M ops/s local_storage cache interleaved get: hits throughput: 50.073 ± 0.609 M ops/s, hits latency: 19.971 ns/op, important_hits throughput: 17.883 ± 0.217 M ops/s num_maps: 16 local_storage cache sequential get: hits throughput: 43.962 ± 0.525 M ops/s, hits latency: 22.747 ns/op, important_hits throughput: 2.748 ± 0.033 M ops/s local_storage cache interleaved get: hits throughput: 48.166 ± 0.825 M ops/s, hits latency: 20.761 ns/op, important_hits throughput: 15.326 ± 0.263 M ops/s num_maps: 17 local_storage cache sequential get: hits throughput: 33.207 ± 0.461 M ops/s, hits latency: 30.114 ns/op, important_hits throughput: 1.956 ± 0.027 M ops/s local_storage cache interleaved get: hits throughput: 43.540 ± 0.265 M ops/s, hits latency: 22.968 ns/op, important_hits throughput: 13.255 ± 0.081 M ops/s num_maps: 24 local_storage cache sequential get: hits throughput: 19.402 ± 0.348 M ops/s, hits latency: 51.542 ns/op, important_hits throughput: 0.809 ± 0.015 M ops/s local_storage cache interleaved get: hits throughput: 22.981 ± 0.487 M ops/s, hits latency: 43.514 ns/op, important_hits throughput: 6.465 ± 0.137 M ops/s num_maps: 32 local_storage cache sequential get: hits throughput: 13.378 ± 0.220 M ops/s, hits latency: 74.748 ns/op, important_hits throughput: 0.419 ± 0.007 M ops/s local_storage cache interleaved get: hits throughput: 16.894 ± 0.172 M ops/s, hits latency: 59.193 ns/op, important_hits throughput: 4.716 ± 0.048 M ops/s num_maps: 100 local_storage cache sequential get: hits throughput: 6.070 ± 0.140 M ops/s, hits latency: 164.745 ns/op, important_hits throughput: 0.061 ± 0.001 M ops/s local_storage cache interleaved get: hits throughput: 7.323 ± 0.149 M ops/s, hits latency: 136.554 ns/op, important_hits throughput: 1.913 ± 0.039 M ops/s num_maps: 1000 local_storage cache sequential get: hits throughput: 0.438 ± 0.012 M ops/s, hits latency: 2281.369 ns/op, important_hits throughput: 0.000 ± 0.000 M ops/s local_storage cache interleaved get: hits throughput: 0.522 ± 0.010 M ops/s, hits latency: 1913.937 ns/op, important_hits throughput: 0.131 ± 0.003 M ops/s Looking at the "sequential get" results, it's clear that as the number of task local_storage maps grows beyond the current cache size (16), there's a significant reduction in hits throughput. Note that current local_storage implementation assigns a cache_idx to maps as they are created. Since "sequential get" is creating maps 0..n in order and then doing bpf_task_storage_get calls in the same order, the benchmark is effectively ensuring that a map will not be in cache when the program tries to access it. For "interleaved get" results, important-map hits throughput is greatly increased as the important map is more likely to be in cache by virtue of being accessed far more frequently. Throughput still reduces as # maps increases, though. To get a sense of the overhead of the benchmark program, I commented out bpf_task_storage_get/bpf_map_lookup_elem in local_storage_bench.c and ran the benchmark on the same host as the 'real' run. Results: Local Storage ============= Hashmap Control w/ 500 maps hashmap (control) sequential get: hits throughput: 96.965 ± 1.346 M ops/s, hits latency: 10.313 ns/op, important_hits throughput: 0.194 ± 0.003 M ops/s num_maps: 1 local_storage cache sequential get: hits throughput: 105.792 ± 1.860 M ops/s, hits latency: 9.453 ns/op, important_hits throughput: 105.792 ± 1.860 M ops/s local_storage cache interleaved get: hits throughput: 185.847 ± 4.014 M ops/s, hits latency: 5.381 ns/op, important_hits throughput: 185.847 ± 4.014 M ops/s num_maps: 10 local_storage cache sequential get: hits throughput: 109.867 ± 1.358 M ops/s, hits latency: 9.102 ns/op, important_hits throughput: 10.987 ± 0.136 M ops/s local_storage cache interleaved get: hits throughput: 144.165 ± 1.256 M ops/s, hits latency: 6.936 ns/op, important_hits throughput: 51.487 ± 0.449 M ops/s num_maps: 16 local_storage cache sequential get: hits throughput: 109.258 ± 1.902 M ops/s, hits latency: 9.153 ns/op, important_hits throughput: 6.829 ± 0.119 M ops/s local_storage cache interleaved get: hits throughput: 140.248 ± 1.836 M ops/s, hits latency: 7.130 ns/op, important_hits throughput: 44.624 ± 0.584 M ops/s num_maps: 17 local_storage cache sequential get: hits throughput: 116.397 ± 7.679 M ops/s, hits latency: 8.591 ns/op, important_hits throughput: 6.856 ± 0.452 M ops/s local_storage cache interleaved get: hits throughput: 128.411 ± 4.927 M ops/s, hits latency: 7.787 ns/op, important_hits throughput: 39.093 ± 1.500 M ops/s num_maps: 24 local_storage cache sequential get: hits throughput: 110.890 ± 0.976 M ops/s, hits latency: 9.018 ns/op, important_hits throughput: 4.624 ± 0.041 M ops/s local_storage cache interleaved get: hits throughput: 133.316 ± 1.889 M ops/s, hits latency: 7.501 ns/op, important_hits throughput: 37.503 ± 0.531 M ops/s num_maps: 32 local_storage cache sequential get: hits throughput: 112.900 ± 1.171 M ops/s, hits latency: 8.857 ns/op, important_hits throughput: 3.534 ± 0.037 M ops/s local_storage cache interleaved get: hits throughput: 132.844 ± 1.207 M ops/s, hits latency: 7.528 ns/op, important_hits throughput: 37.081 ± 0.337 M ops/s num_maps: 100 local_storage cache sequential get: hits throughput: 110.025 ± 4.714 M ops/s, hits latency: 9.089 ns/op, important_hits throughput: 1.100 ± 0.047 M ops/s local_storage cache interleaved get: hits throughput: 131.979 ± 5.013 M ops/s, hits latency: 7.577 ns/op, important_hits throughput: 34.472 ± 1.309 M ops/s num_maps: 1000 local_storage cache sequential get: hits throughput: 117.850 ± 2.423 M ops/s, hits latency: 8.485 ns/op, important_hits throughput: 0.118 ± 0.002 M ops/s local_storage cache interleaved get: hits throughput: 141.268 ± 9.658 M ops/s, hits latency: 7.079 ns/op, important_hits throughput: 35.476 ± 2.425 M ops/s Adjusting for overhead, latency numbers for "hashmap control" and "sequential get" are: hashmap_control: ~10.4ns sequential_get_1: ~13.0ns sequential_get_10: ~13.8ns sequential_get_16: ~13.6ns sequential_get_17: ~21.5ns sequential_get_24: ~42.5ns sequential_get_32: ~65.9ns sequential_get_100: ~155.7ns sequential_get_1000: ~2270ns Clearly demonstrating a cliff. When running the benchmarks it may be necessary to bump 'open files' ulimit for a successful run. [0]: https://lore.kernel.org/all/20220420002143.1096548-1-davemarchevsky@fb.com Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com> --- Changelog: v3 -> v4: * Remove ifs guarding increments in measure fn (Andrii) * Refactor to use 1 bpf prog for all 3 benchmarks w/ global vars set from userspace before load to control behavior (Andrii) * Greatly reduce variance in overhead by having benchmark bpf prog loop 10k times regardless of map count (Andrii) * Also, move sync_fetch_and_incr out of do_lookup as the guaranteed second sync_fetch_and_incr call for num_maps = 1 was adding overhead * Add second patch refactoring bench.c's mean/stddev calculations in reporting helper fns v2 -> v3: * Accessing 1k maps in ARRAY_OF_MAPS doesn't hit MAX_USED_MAPS limit, so just use 1 program (Alexei) v1 -> v2: * Adopt ARRAY_OF_MAPS approach for bpf program, allowing truly configurable # of maps (Andrii) * Add hashmap benchmark (Alexei) * Add discussion of overhead tools/testing/selftests/bpf/Makefile | 4 +- tools/testing/selftests/bpf/bench.c | 55 ++++ tools/testing/selftests/bpf/bench.h | 4 + .../bpf/benchs/bench_local_storage.c | 250 ++++++++++++++++++ .../bpf/benchs/run_bench_local_storage.sh | 21 ++ .../selftests/bpf/benchs/run_common.sh | 17 ++ .../selftests/bpf/progs/local_storage_bench.c | 99 +++++++ 7 files changed, 449 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/benchs/bench_local_storage.c create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_local_storage.sh create mode 100644 tools/testing/selftests/bpf/progs/local_storage_bench.c