| Message ID | 20220909124300.3409187-2-coltonlewis@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: selftests: randomize memory access of dirty_log_perf_test | expand |
On Fri, Sep 09, 2022 at 12:42:58PM +0000, Colton Lewis wrote: > Implement random number generation for guest code to randomize parts > of the test, making it less predictable and a more accurate reflection > of reality. > > Create a -r argument to specify a random seed. If no argument is > provided, the seed defaults to the current Unix timestamp. The random > seed is set with perf_test_set_random_seed() and must be set before > guest_code runs to apply. > > The random number generator chosen is the Park-Miller Linear > Congruential Generator, a fancy name for a basic and well-understood > random number generator entirely sufficient for this purpose. Each > vCPU calculates its own seed by adding its index to the seed provided. > Reviewed-by: Ricardo Koller <ricarkol@google.com> > Signed-off-by: Colton Lewis <coltonlewis@google.com> > --- > tools/testing/selftests/kvm/dirty_log_perf_test.c | 12 ++++++++++-- > tools/testing/selftests/kvm/include/perf_test_util.h | 2 ++ > tools/testing/selftests/kvm/include/test_util.h | 2 ++ > tools/testing/selftests/kvm/lib/perf_test_util.c | 11 ++++++++++- > tools/testing/selftests/kvm/lib/test_util.c | 9 +++++++++ > 5 files changed, 33 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c > index d60a34cdfaee..2f91acd94130 100644 > --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c > +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c > @@ -126,6 +126,7 @@ struct test_params { > bool partition_vcpu_memory_access; > enum vm_mem_backing_src_type backing_src; > int slots; > + uint32_t random_seed; > }; > > static void toggle_dirty_logging(struct kvm_vm *vm, int slots, bool enable) > @@ -220,6 +221,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) > p->slots, p->backing_src, > p->partition_vcpu_memory_access); > > + pr_info("Random seed: %u\n", p->random_seed); > + perf_test_set_random_seed(vm, p->random_seed); > perf_test_set_wr_fract(vm, p->wr_fract); > > guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm); > @@ -337,7 +340,7 @@ static void help(char *name) > { > puts(""); > printf("usage: %s [-h] [-i iterations] [-p offset] [-g] " > - "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-s mem type]" > + "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]" > "[-x memslots]\n", name); > puts(""); > printf(" -i: specify iteration counts (default: %"PRIu64")\n", > @@ -362,6 +365,7 @@ static void help(char *name) > printf(" -v: specify the number of vCPUs to run.\n"); > printf(" -o: Overlap guest memory accesses instead of partitioning\n" > " them into a separate region of memory for each vCPU.\n"); > + printf(" -r: specify the starting random seed.\n"); > backing_src_help("-s"); > printf(" -x: Split the memory region into this number of memslots.\n" > " (default: 1)\n"); > @@ -378,6 +382,7 @@ int main(int argc, char *argv[]) > .partition_vcpu_memory_access = true, > .backing_src = DEFAULT_VM_MEM_SRC, > .slots = 1, > + .random_seed = time(NULL), > }; > int opt; > > @@ -388,7 +393,7 @@ int main(int argc, char *argv[]) > > guest_modes_append_default(); > > - while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:os:x:")) != -1) { > + while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:or:s:x:")) != -1) { > switch (opt) { > case 'g': > dirty_log_manual_caps = 0; > @@ -421,6 +426,9 @@ int main(int argc, char *argv[]) > case 'o': > p.partition_vcpu_memory_access = false; > break; > + case 'r': > + p.random_seed = atoi(optarg); > + break; > case 's': > p.backing_src = parse_backing_src_type(optarg); > break; > diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h > index d822cb670f1c..f18530984b42 100644 > --- a/tools/testing/selftests/kvm/include/perf_test_util.h > +++ b/tools/testing/selftests/kvm/include/perf_test_util.h > @@ -34,6 +34,7 @@ struct perf_test_args { > uint64_t gpa; > uint64_t size; > uint64_t guest_page_size; > + uint32_t random_seed; > int wr_fract; > > /* Run vCPUs in L2 instead of L1, if the architecture supports it. */ > @@ -51,6 +52,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, > void perf_test_destroy_vm(struct kvm_vm *vm); > > void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract); > +void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed); > > void perf_test_start_vcpu_threads(int vcpus, void (*vcpu_fn)(struct perf_test_vcpu_args *)); > void perf_test_join_vcpu_threads(int vcpus); > diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h > index 99e0dcdc923f..2dd286bcf46f 100644 > --- a/tools/testing/selftests/kvm/include/test_util.h > +++ b/tools/testing/selftests/kvm/include/test_util.h > @@ -143,4 +143,6 @@ static inline void *align_ptr_up(void *x, size_t size) > return (void *)align_up((unsigned long)x, size); > } > > +void guest_random(uint32_t *seed); > + > #endif /* SELFTEST_KVM_TEST_UTIL_H */ > diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c > index f989ff91f022..4d9c7d7693d9 100644 > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c > @@ -47,6 +47,7 @@ void perf_test_guest_code(uint32_t vcpu_id) > uint64_t gva; > uint64_t pages; > int i; > + uint32_t rand = pta->random_seed + vcpu_id; > > /* Make sure vCPU args data structure is not corrupt. */ > GUEST_ASSERT(vcpu_args->vcpu_id == vcpu_id); > @@ -57,6 +58,7 @@ void perf_test_guest_code(uint32_t vcpu_id) > while (true) { > for (i = 0; i < pages; i++) { > uint64_t addr = gva + (i * pta->guest_page_size); > + guest_random(&rand); > > if (i % pta->wr_fract == 0) > *(uint64_t *)addr = 0x0123456789ABCDEF; > @@ -115,8 +117,9 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, > > pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode)); > > - /* By default vCPUs will write to memory. */ > + /* Set perf_test_args defaults. */ > pta->wr_fract = 1; > + pta->random_seed = time(NULL); > > /* > * Snapshot the non-huge page size. This is used by the guest code to > @@ -224,6 +227,12 @@ void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract) > sync_global_to_guest(vm, perf_test_args); > } > > +void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed) > +{ > + perf_test_args.random_seed = random_seed; > + sync_global_to_guest(vm, perf_test_args.random_seed); > +} > + > uint64_t __weak perf_test_nested_pages(int nr_vcpus) > { > return 0; > diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c > index 6d23878bbfe1..28c895743abe 100644 > --- a/tools/testing/selftests/kvm/lib/test_util.c > +++ b/tools/testing/selftests/kvm/lib/test_util.c > @@ -17,6 +17,15 @@ > > #include "test_util.h" > > +/* > + * Random number generator that is usable from guest code. This is the > + * Park-Miller LCG using standard constants. > + */ > +void guest_random(uint32_t *seed) > +{ > + *seed = (uint64_t)*seed * 48271 % ((uint32_t)(1 << 31) - 1); > +} > + > /* > * Parses "[0-9]+[kmgt]?". > */ > -- > 2.37.2.789.g6183377224-goog >
On Fri, Sep 09, 2022 at 12:42:58PM +0000, Colton Lewis wrote: > Implement random number generation for guest code to randomize parts > of the test, making it less predictable and a more accurate reflection > of reality. > > Create a -r argument to specify a random seed. If no argument is > provided, the seed defaults to the current Unix timestamp. The random > seed is set with perf_test_set_random_seed() and must be set before > guest_code runs to apply. > > The random number generator chosen is the Park-Miller Linear > Congruential Generator, a fancy name for a basic and well-understood > random number generator entirely sufficient for this purpose. Each > vCPU calculates its own seed by adding its index to the seed provided. Great commit message! > > Signed-off-by: Colton Lewis <coltonlewis@google.com> > --- > tools/testing/selftests/kvm/dirty_log_perf_test.c | 12 ++++++++++-- > tools/testing/selftests/kvm/include/perf_test_util.h | 2 ++ > tools/testing/selftests/kvm/include/test_util.h | 2 ++ > tools/testing/selftests/kvm/lib/perf_test_util.c | 11 ++++++++++- > tools/testing/selftests/kvm/lib/test_util.c | 9 +++++++++ > 5 files changed, 33 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c > index d60a34cdfaee..2f91acd94130 100644 > --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c > +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c > @@ -126,6 +126,7 @@ struct test_params { > bool partition_vcpu_memory_access; > enum vm_mem_backing_src_type backing_src; > int slots; > + uint32_t random_seed; > }; > > static void toggle_dirty_logging(struct kvm_vm *vm, int slots, bool enable) > @@ -220,6 +221,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) > p->slots, p->backing_src, > p->partition_vcpu_memory_access); > > + pr_info("Random seed: %u\n", p->random_seed); > + perf_test_set_random_seed(vm, p->random_seed); > perf_test_set_wr_fract(vm, p->wr_fract); > > guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm); > @@ -337,7 +340,7 @@ static void help(char *name) > { > puts(""); > printf("usage: %s [-h] [-i iterations] [-p offset] [-g] " > - "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-s mem type]" > + "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]" > "[-x memslots]\n", name); > puts(""); > printf(" -i: specify iteration counts (default: %"PRIu64")\n", > @@ -362,6 +365,7 @@ static void help(char *name) > printf(" -v: specify the number of vCPUs to run.\n"); > printf(" -o: Overlap guest memory accesses instead of partitioning\n" > " them into a separate region of memory for each vCPU.\n"); > + printf(" -r: specify the starting random seed.\n"); > backing_src_help("-s"); > printf(" -x: Split the memory region into this number of memslots.\n" > " (default: 1)\n"); > @@ -378,6 +382,7 @@ int main(int argc, char *argv[]) > .partition_vcpu_memory_access = true, > .backing_src = DEFAULT_VM_MEM_SRC, > .slots = 1, > + .random_seed = time(NULL), It's a bad code smell that the random seed gets default initialized to time(NULL) twice (here and in perf_test_create_vm()). I also still think it would be better if the default random seed was consistent across runs. Most use-cases of dirty_log_perf_test is for A/B testing, so consistency is key. For example, running dirty_log_perf_test at every commit to find regressions, or running dirty_log_perf_test to study the performance effects of some change. In other words, I think most use-cases will want a consistent seed across runs, so the default behavior should match that. Otherwise I forsee myself (and automated tools) having to pass in -r to every test runs to get consistent, comparable, behavior. What do you think about killing 2 birds with one stone here and make the default random_seed 0. That requires no initialization and ensures consistent random behavior across runs. And then optionally... I would even recommend dropping the -r parameter until someone wants to run dirty_log_perf_test with different seeds. That would simplify the code even more. I have a feeling there won't be much interest in different seeds since, at the end of the day, it will always be the same rough distribution of accesses. More interesting than different seeds will be adding support for different types of access patterns.
diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c index d60a34cdfaee..2f91acd94130 100644 --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c @@ -126,6 +126,7 @@ struct test_params { bool partition_vcpu_memory_access; enum vm_mem_backing_src_type backing_src; int slots; + uint32_t random_seed; }; static void toggle_dirty_logging(struct kvm_vm *vm, int slots, bool enable) @@ -220,6 +221,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) p->slots, p->backing_src, p->partition_vcpu_memory_access); + pr_info("Random seed: %u\n", p->random_seed); + perf_test_set_random_seed(vm, p->random_seed); perf_test_set_wr_fract(vm, p->wr_fract); guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm); @@ -337,7 +340,7 @@ static void help(char *name) { puts(""); printf("usage: %s [-h] [-i iterations] [-p offset] [-g] " - "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-s mem type]" + "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]" "[-x memslots]\n", name); puts(""); printf(" -i: specify iteration counts (default: %"PRIu64")\n", @@ -362,6 +365,7 @@ static void help(char *name) printf(" -v: specify the number of vCPUs to run.\n"); printf(" -o: Overlap guest memory accesses instead of partitioning\n" " them into a separate region of memory for each vCPU.\n"); + printf(" -r: specify the starting random seed.\n"); backing_src_help("-s"); printf(" -x: Split the memory region into this number of memslots.\n" " (default: 1)\n"); @@ -378,6 +382,7 @@ int main(int argc, char *argv[]) .partition_vcpu_memory_access = true, .backing_src = DEFAULT_VM_MEM_SRC, .slots = 1, + .random_seed = time(NULL), }; int opt; @@ -388,7 +393,7 @@ int main(int argc, char *argv[]) guest_modes_append_default(); - while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:os:x:")) != -1) { + while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:or:s:x:")) != -1) { switch (opt) { case 'g': dirty_log_manual_caps = 0; @@ -421,6 +426,9 @@ int main(int argc, char *argv[]) case 'o': p.partition_vcpu_memory_access = false; break; + case 'r': + p.random_seed = atoi(optarg); + break; case 's': p.backing_src = parse_backing_src_type(optarg); break; diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h index d822cb670f1c..f18530984b42 100644 --- a/tools/testing/selftests/kvm/include/perf_test_util.h +++ b/tools/testing/selftests/kvm/include/perf_test_util.h @@ -34,6 +34,7 @@ struct perf_test_args { uint64_t gpa; uint64_t size; uint64_t guest_page_size; + uint32_t random_seed; int wr_fract; /* Run vCPUs in L2 instead of L1, if the architecture supports it. */ @@ -51,6 +52,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, void perf_test_destroy_vm(struct kvm_vm *vm); void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract); +void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed); void perf_test_start_vcpu_threads(int vcpus, void (*vcpu_fn)(struct perf_test_vcpu_args *)); void perf_test_join_vcpu_threads(int vcpus); diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h index 99e0dcdc923f..2dd286bcf46f 100644 --- a/tools/testing/selftests/kvm/include/test_util.h +++ b/tools/testing/selftests/kvm/include/test_util.h @@ -143,4 +143,6 @@ static inline void *align_ptr_up(void *x, size_t size) return (void *)align_up((unsigned long)x, size); } +void guest_random(uint32_t *seed); + #endif /* SELFTEST_KVM_TEST_UTIL_H */ diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c index f989ff91f022..4d9c7d7693d9 100644 --- a/tools/testing/selftests/kvm/lib/perf_test_util.c +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c @@ -47,6 +47,7 @@ void perf_test_guest_code(uint32_t vcpu_id) uint64_t gva; uint64_t pages; int i; + uint32_t rand = pta->random_seed + vcpu_id; /* Make sure vCPU args data structure is not corrupt. */ GUEST_ASSERT(vcpu_args->vcpu_id == vcpu_id); @@ -57,6 +58,7 @@ void perf_test_guest_code(uint32_t vcpu_id) while (true) { for (i = 0; i < pages; i++) { uint64_t addr = gva + (i * pta->guest_page_size); + guest_random(&rand); if (i % pta->wr_fract == 0) *(uint64_t *)addr = 0x0123456789ABCDEF; @@ -115,8 +117,9 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode)); - /* By default vCPUs will write to memory. */ + /* Set perf_test_args defaults. */ pta->wr_fract = 1; + pta->random_seed = time(NULL); /* * Snapshot the non-huge page size. This is used by the guest code to @@ -224,6 +227,12 @@ void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract) sync_global_to_guest(vm, perf_test_args); } +void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed) +{ + perf_test_args.random_seed = random_seed; + sync_global_to_guest(vm, perf_test_args.random_seed); +} + uint64_t __weak perf_test_nested_pages(int nr_vcpus) { return 0; diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c index 6d23878bbfe1..28c895743abe 100644 --- a/tools/testing/selftests/kvm/lib/test_util.c +++ b/tools/testing/selftests/kvm/lib/test_util.c @@ -17,6 +17,15 @@ #include "test_util.h" +/* + * Random number generator that is usable from guest code. This is the + * Park-Miller LCG using standard constants. + */ +void guest_random(uint32_t *seed) +{ + *seed = (uint64_t)*seed * 48271 % ((uint32_t)(1 << 31) - 1); +} + /* * Parses "[0-9]+[kmgt]?". */
Implement random number generation for guest code to randomize parts of the test, making it less predictable and a more accurate reflection of reality. Create a -r argument to specify a random seed. If no argument is provided, the seed defaults to the current Unix timestamp. The random seed is set with perf_test_set_random_seed() and must be set before guest_code runs to apply. The random number generator chosen is the Park-Miller Linear Congruential Generator, a fancy name for a basic and well-understood random number generator entirely sufficient for this purpose. Each vCPU calculates its own seed by adding its index to the seed provided. Signed-off-by: Colton Lewis <coltonlewis@google.com> --- tools/testing/selftests/kvm/dirty_log_perf_test.c | 12 ++++++++++-- tools/testing/selftests/kvm/include/perf_test_util.h | 2 ++ tools/testing/selftests/kvm/include/test_util.h | 2 ++ tools/testing/selftests/kvm/lib/perf_test_util.c | 11 ++++++++++- tools/testing/selftests/kvm/lib/test_util.c | 9 +++++++++ 5 files changed, 33 insertions(+), 3 deletions(-)