| Message ID | 20230914221526.3153402-10-dhowells@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iov_iter: kunit: Cleanup, abstraction and more tests | expand |
From: David Howells > Sent: 14 September 2023 23:15 > > Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC > iterator. This attaches a userspace VM with a mapped file in it > temporarily to the test thread. Isn't that going to be completely dominated by the cache fills from memory? I'd have thought you'd need to use something with a lot of small fragments so that the iteration code dominates the copy. Some measurements can be made using readv() and writev() on /dev/zero and /dev/null. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
David Laight <David.Laight@ACULAB.COM> wrote: > > Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC > > iterator. This attaches a userspace VM with a mapped file in it > > temporarily to the test thread. > > Isn't that going to be completely dominated by the cache fills > from memory? Yes... but it should be consistent in the amount of time that consumes since no device drivers are involved. I can try adding the same folio to the anon_file multiple times - it might work especially if I don't put the pages on the LRU (if that's even possible) - but I wanted separate pages for the extraction test. > I'd have thought you'd need to use something with a lot of > small fragments so that the iteration code dominates the copy. That would actually be a separate benchmark case which I should try also. > Some measurements can be made using readv() and writev() > on /dev/zero and /dev/null. Forget /dev/null; that doesn't actually engage any iteration code. The same for writing to /dev/zero. Reading from /dev/zero does its own iteration thing rather than using iterate_and_advance(), presumably because it checks for signals and resched. David
From: David Howells > Sent: 15 September 2023 11:10 > > David Laight <David.Laight@ACULAB.COM> wrote: > > > > Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC > > > iterator. This attaches a userspace VM with a mapped file in it > > > temporarily to the test thread. > > > > Isn't that going to be completely dominated by the cache fills > > from memory? > > Yes... but it should be consistent in the amount of time that consumes since > no device drivers are involved. I can try adding the same folio to the > anon_file multiple times - it might work especially if I don't put the pages > on the LRU (if that's even possible) - but I wanted separate pages for the > extraction test. You could also just not do the copy! Although you need (say) asm volatile("\n",:::"memory") to stop it all being completely optimised away. That might show up a difference in the 'out_of_line' test where 15% on top on the data copies is massive - it may be that the data cache behaviour is very different for the two cases. ... > > Some measurements can be made using readv() and writev() > > on /dev/zero and /dev/null. > > Forget /dev/null; that doesn't actually engage any iteration code. The same > for writing to /dev/zero. Reading from /dev/zero does its own iteration thing > rather than using iterate_and_advance(), presumably because it checks for > signals and resched. Using /dev/null does exercise the 'copy iov from user' code. Last time I looked at that the 32bit compat code was faster than the 64bit code on x86! David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
David Laight <David.Laight@ACULAB.COM> wrote: > > > Some measurements can be made using readv() and writev() > > > on /dev/zero and /dev/null. > > > > Forget /dev/null; that doesn't actually engage any iteration code. The same > > for writing to /dev/zero. Reading from /dev/zero does its own iteration thing > > rather than using iterate_and_advance(), presumably because it checks for > > signals and resched. > > Using /dev/null does exercise the 'copy iov from user' code. Ummm.... Not really: static ssize_t read_null(struct file *file, char __user *buf, size_t count, loff_t *ppos) { return 0; } static ssize_t write_null(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { return count; } static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to) { return 0; } static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from) { size_t count = iov_iter_count(from); iov_iter_advance(from, count); return count; } David
From: David Howells > Sent: 15 September 2023 12:23 > > David Laight <David.Laight@ACULAB.COM> wrote: > > > > > Some measurements can be made using readv() and writev() > > > > on /dev/zero and /dev/null. > > > > > > Forget /dev/null; that doesn't actually engage any iteration code. The same > > > for writing to /dev/zero. Reading from /dev/zero does its own iteration thing > > > rather than using iterate_and_advance(), presumably because it checks for > > > signals and resched. > > > > Using /dev/null does exercise the 'copy iov from user' code. > > Ummm.... Not really: I was thinking of import_iovec() - or whatever its current name is. That really needs a single structure that contains the iov_iter and the cache[] (which the caller pretty much always allocates in the same place). Fiddling with that is ok until you find what io_uring does. Then it all gets entirely horrid. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
David Laight <David.Laight@ACULAB.COM> wrote: > Isn't that going to be completely dominated by the cache fills > from memory? > > I'd have thought you'd need to use something with a lot of > small fragments so that the iteration code dominates the copy. Okay, if I switch it to using MAP_ANON for the big 256MiB buffer, switch all the benchmarking tests to use copy_from_iter() rather than copy_to_iter() and make the iovec benchmark use a separate iovec for each page, there's then a single page replicated across the mapping. Given that, without my macro-to-inline-func patches applied, I see: iov_kunit_benchmark_bvec: avg 3184 uS, stddev 16 uS iov_kunit_benchmark_bvec: avg 3189 uS, stddev 17 uS iov_kunit_benchmark_bvec: avg 3190 uS, stddev 16 uS iov_kunit_benchmark_bvec_outofline: avg 3731 uS, stddev 10 uS iov_kunit_benchmark_bvec_outofline: avg 3735 uS, stddev 10 uS iov_kunit_benchmark_bvec_outofline: avg 3738 uS, stddev 11 uS iov_kunit_benchmark_bvec_split: avg 3403 uS, stddev 10 uS iov_kunit_benchmark_bvec_split: avg 3405 uS, stddev 18 uS iov_kunit_benchmark_bvec_split: avg 3407 uS, stddev 29 uS iov_kunit_benchmark_iovec: avg 6616 uS, stddev 20 uS iov_kunit_benchmark_iovec: avg 6619 uS, stddev 22 uS iov_kunit_benchmark_iovec: avg 6621 uS, stddev 46 uS iov_kunit_benchmark_kvec: avg 2671 uS, stddev 12 uS iov_kunit_benchmark_kvec: avg 2671 uS, stddev 13 uS iov_kunit_benchmark_kvec: avg 2675 uS, stddev 12 uS iov_kunit_benchmark_ubuf: avg 6191 uS, stddev 1946 uS iov_kunit_benchmark_ubuf: avg 6418 uS, stddev 3263 uS iov_kunit_benchmark_ubuf: avg 6443 uS, stddev 3275 uS iov_kunit_benchmark_xarray: avg 3689 uS, stddev 5 uS iov_kunit_benchmark_xarray: avg 3689 uS, stddev 6 uS iov_kunit_benchmark_xarray: avg 3698 uS, stddev 22 uS iov_kunit_benchmark_xarray_outofline: avg 4202 uS, stddev 3 uS iov_kunit_benchmark_xarray_outofline: avg 4204 uS, stddev 9 uS iov_kunit_benchmark_xarray_outofline: avg 4210 uS, stddev 9 uS and with, I get: iov_kunit_benchmark_bvec: avg 3241 uS, stddev 13 uS iov_kunit_benchmark_bvec: avg 3245 uS, stddev 16 uS iov_kunit_benchmark_bvec: avg 3248 uS, stddev 15 uS iov_kunit_benchmark_bvec_outofline: avg 3705 uS, stddev 12 uS iov_kunit_benchmark_bvec_outofline: avg 3706 uS, stddev 10 uS iov_kunit_benchmark_bvec_outofline: avg 3709 uS, stddev 9 uS iov_kunit_benchmark_bvec_split: avg 3446 uS, stddev 10 uS iov_kunit_benchmark_bvec_split: avg 3447 uS, stddev 12 uS iov_kunit_benchmark_bvec_split: avg 3448 uS, stddev 12 uS iov_kunit_benchmark_iovec: avg 6587 uS, stddev 22 uS iov_kunit_benchmark_iovec: avg 6587 uS, stddev 22 uS iov_kunit_benchmark_iovec: avg 6590 uS, stddev 27 uS iov_kunit_benchmark_kvec: avg 2671 uS, stddev 12 uS iov_kunit_benchmark_kvec: avg 2672 uS, stddev 12 uS iov_kunit_benchmark_kvec: avg 2676 uS, stddev 19 uS iov_kunit_benchmark_ubuf: avg 6241 uS, stddev 2199 uS iov_kunit_benchmark_ubuf: avg 6266 uS, stddev 2245 uS iov_kunit_benchmark_ubuf: avg 6513 uS, stddev 3899 uS iov_kunit_benchmark_xarray: avg 3695 uS, stddev 6 uS iov_kunit_benchmark_xarray: avg 3695 uS, stddev 7 uS iov_kunit_benchmark_xarray: avg 3703 uS, stddev 11 uS iov_kunit_benchmark_xarray_outofline: avg 4215 uS, stddev 16 uS iov_kunit_benchmark_xarray_outofline: avg 4217 uS, stddev 20 uS iov_kunit_benchmark_xarray_outofline: avg 4224 uS, stddev 10 uS Interestingly, most of them are quite tight, but UBUF is all over the place. That's with the test covering the entire 256M span with a single UBUF iterator, so it would seem unlikely that the difference is due to the iteration framework. David
David Laight <David.Laight@ACULAB.COM> wrote: > I was thinking of import_iovec() - or whatever its current > name is. That doesn't actually access the buffer described by the iovec[]. > That really needs a single structure that contains the iov_iter > and the cache[] (which the caller pretty much always allocates > in the same place). cache[]? > Fiddling with that is ok until you find what io_uring does. > Then it all gets entirely horrid. That statement sounds like back-of-the-OLS-T-shirt material ;-) David
From: David Howells > Sent: 15 September 2023 13:36 > > David Laight <David.Laight@ACULAB.COM> wrote: > > > I was thinking of import_iovec() - or whatever its current > > name is. > > That doesn't actually access the buffer described by the iovec[]. > > > That really needs a single structure that contains the iov_iter > > and the cache[] (which the caller pretty much always allocates > > in the same place). > > cache[]? Ah it is usually called iovstack[]. That is the code that reads the iovec[] from user. For small counts there is an on-stack cache[], for large counts it has call kmalloc(). So when the io completes you have to free the allocated buffer. A canonical example is: static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec, unsigned long vlen, loff_t *pos, rwf_t flags) { struct iovec iovstack[UIO_FASTIOV]; struct iovec *iov = iovstack; struct iov_iter iter; ssize_t ret; ret = import_iovec(ITER_DEST, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter); if (ret >= 0) { ret = do_iter_read(file, &iter, pos, flags); kfree(iov); } return ret; } If 'iter' and 'iovstack' are put together in a structure the calling sequence becomes much less annoying. The kfree() can (probably) check iter.iovec != iovsatack (as an inline). But io_uring manages to allocate the iov_iter and iovstack[] in entirely different places - and then copies them about. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
David Laight <David.Laight@ACULAB.COM> wrote: > You could also just not do the copy! > Although you need (say) asm volatile("\n",:::"memory") to > stop it all being completely optimised away. > That might show up a difference in the 'out_of_line' test > where 15% on top on the data copies is massive - it may be > that the data cache behaviour is very different for the > two cases. I tried using the following as the load: volatile unsigned long foo; static __always_inline size_t idle_user_iter(void __user *iter_from, size_t progress, size_t len, void *to, void *priv2) { nop(); nop(); foo += (unsigned long)iter_from; foo += (unsigned long)len; foo += (unsigned long)to + progress; nop(); nop(); return 0; } static __always_inline size_t idle_kernel_iter(void *iter_from, size_t progress, size_t len, void *to, void *priv2) { nop(); nop(); foo += (unsigned long)iter_from; foo += (unsigned long)len; foo += (unsigned long)to + progress; nop(); nop(); return 0; } size_t iov_iter_idle(struct iov_iter *iter, size_t len, void *priv) { return iterate_and_advance(iter, len, priv, idle_user_iter, idle_kernel_iter); } EXPORT_SYMBOL(iov_iter_idle); adding various things into a volatile variable to prevent the optimiser from discarding the calculations. I get: iov_kunit_benchmark_bvec: avg 395 uS, stddev 46 uS iov_kunit_benchmark_bvec: avg 397 uS, stddev 38 uS iov_kunit_benchmark_bvec: avg 411 uS, stddev 57 uS iov_kunit_benchmark_bvec_outofline: avg 781 uS, stddev 5 uS iov_kunit_benchmark_bvec_outofline: avg 781 uS, stddev 6 uS iov_kunit_benchmark_bvec_outofline: avg 781 uS, stddev 7 uS iov_kunit_benchmark_bvec_split: avg 3599 uS, stddev 737 uS iov_kunit_benchmark_bvec_split: avg 3664 uS, stddev 838 uS iov_kunit_benchmark_bvec_split: avg 3669 uS, stddev 875 uS iov_kunit_benchmark_iovec: avg 472 uS, stddev 17 uS iov_kunit_benchmark_iovec: avg 506 uS, stddev 59 uS iov_kunit_benchmark_iovec: avg 525 uS, stddev 14 uS iov_kunit_benchmark_kvec: avg 421 uS, stddev 73 uS iov_kunit_benchmark_kvec: avg 428 uS, stddev 68 uS iov_kunit_benchmark_kvec: avg 469 uS, stddev 75 uS iov_kunit_benchmark_ubuf: avg 1052 uS, stddev 6 uS iov_kunit_benchmark_ubuf: avg 1168 uS, stddev 8 uS iov_kunit_benchmark_ubuf: avg 1168 uS, stddev 9 uS iov_kunit_benchmark_xarray: avg 680 uS, stddev 11 uS iov_kunit_benchmark_xarray: avg 682 uS, stddev 20 uS iov_kunit_benchmark_xarray: avg 686 uS, stddev 46 uS iov_kunit_benchmark_xarray_outofline: avg 1340 uS, stddev 34 uS iov_kunit_benchmark_xarray_outofline: avg 1358 uS, stddev 12 uS iov_kunit_benchmark_xarray_outofline: avg 1358 uS, stddev 15 uS where I made the iovec and kvec tests split their buffers into PAGE_SIZE segments and the ubuf test issue an iteration per PAGE_SIZE'd chunk. Splitting kvec into just 8 results in the iteration taking <1uS. The bvec_split test is doing a kmalloc() per 256 pages inside of the loop, which is why that takes quite a long time. David
diff --git a/lib/kunit_iov_iter.c b/lib/kunit_iov_iter.c index f8d0cd6a2923..cc9c64663a73 100644 --- a/lib/kunit_iov_iter.c +++ b/lib/kunit_iov_iter.c @@ -1304,6 +1304,89 @@ static void *__init iov_kunit_create_source(struct kunit *test, size_t npages) return scratch; } +/* + * Time copying 256MiB through an ITER_UBUF. + */ +static void __init iov_kunit_benchmark_ubuf(struct kunit *test) +{ + struct iov_iter iter; + unsigned int samples[IOV_KUNIT_NR_SAMPLES]; + ktime_t a, b; + ssize_t copied; + size_t size = 256 * 1024 * 1024, npages = size / PAGE_SIZE; + void *scratch; + int i; + u8 __user *buffer; + + /* Allocate a huge buffer and populate it with pages. */ + buffer = iov_kunit_create_user_buf(test, npages, NULL); + + /* Create a single large buffer to copy to/from. */ + scratch = iov_kunit_create_source(test, npages); + + /* Perform and time a bunch of copies. */ + kunit_info(test, "Benchmarking copy_to_iter() over UBUF:\n"); + for (i = 0; i < IOV_KUNIT_NR_SAMPLES; i++) { + iov_iter_ubuf(&iter, ITER_DEST, buffer, size); + + a = ktime_get_real(); + copied = copy_to_iter(scratch, size, &iter); + b = ktime_get_real(); + KUNIT_EXPECT_EQ(test, copied, size); + samples[i] = ktime_to_us(ktime_sub(b, a)); + } + + iov_kunit_benchmark_print_stats(test, samples); + KUNIT_SUCCEED(); +} + +/* + * Time copying 256MiB through an ITER_IOVEC. + */ +static void __init iov_kunit_benchmark_iovec(struct kunit *test) +{ + struct iov_iter iter; + struct iovec iov[8]; + unsigned int samples[IOV_KUNIT_NR_SAMPLES]; + ktime_t a, b; + ssize_t copied; + size_t size = 256 * 1024 * 1024, npages = size / PAGE_SIZE, part; + void *scratch; + int i; + u8 __user *buffer; + + /* Allocate a huge buffer and populate it with pages. */ + buffer = iov_kunit_create_user_buf(test, npages, NULL); + + /* Create a single large buffer to copy to/from. */ + scratch = iov_kunit_create_source(test, npages); + + /* Split the target over a number of iovecs */ + copied = 0; + for (i = 0; i < ARRAY_SIZE(iov); i++) { + part = size / ARRAY_SIZE(iov); + iov[i].iov_base = buffer + copied; + iov[i].iov_len = part; + copied += part; + } + iov[i - 1].iov_len += size - part; + + /* Perform and time a bunch of copies. */ + kunit_info(test, "Benchmarking copy_to_iter() over IOVEC:\n"); + for (i = 0; i < IOV_KUNIT_NR_SAMPLES; i++) { + iov_iter_init(&iter, ITER_DEST, iov, ARRAY_SIZE(iov), size); + + a = ktime_get_real(); + copied = copy_to_iter(scratch, size, &iter); + b = ktime_get_real(); + KUNIT_EXPECT_EQ(test, copied, size); + samples[i] = ktime_to_us(ktime_sub(b, a)); + } + + iov_kunit_benchmark_print_stats(test, samples); + KUNIT_SUCCEED(); +} + /* * Time copying 256MiB through an ITER_KVEC. */ @@ -1504,6 +1587,8 @@ static struct kunit_case __refdata iov_kunit_cases[] = { KUNIT_CASE(iov_kunit_extract_pages_kvec), KUNIT_CASE(iov_kunit_extract_pages_bvec), KUNIT_CASE(iov_kunit_extract_pages_xarray), + KUNIT_CASE(iov_kunit_benchmark_ubuf), + KUNIT_CASE(iov_kunit_benchmark_iovec), KUNIT_CASE(iov_kunit_benchmark_kvec), KUNIT_CASE(iov_kunit_benchmark_bvec), KUNIT_CASE(iov_kunit_benchmark_bvec_split),
Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC iterator. This attaches a userspace VM with a mapped file in it temporarily to the test thread. Signed-off-by: David Howells <dhowells@redhat.com> cc: Andrew Morton <akpm@linux-foundation.org> cc: Christoph Hellwig <hch@lst.de> cc: Christian Brauner <brauner@kernel.org> cc: Jens Axboe <axboe@kernel.dk> cc: Al Viro <viro@zeniv.linux.org.uk> cc: Matthew Wilcox <willy@infradead.org> cc: David Hildenbrand <david@redhat.com> cc: John Hubbard <jhubbard@nvidia.com> cc: Brendan Higgins <brendanhiggins@google.com> cc: David Gow <davidgow@google.com> cc: linux-kselftest@vger.kernel.org cc: kunit-dev@googlegroups.com cc: linux-mm@kvack.org cc: linux-fsdevel@vger.kernel.org --- lib/kunit_iov_iter.c | 85 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 85 insertions(+)