On 2021-08-06 16:10:29, Zhansaya Bagdauletkyzy wrote: > Since merged pages are copied every time they need to be modified, > the write access time is different between shared and non-shared pages. > Add ksm_cow_time() function which evaluates latency of these COW > breaks. First, 4000 pages are allocated and the time, required to modify > 1 byte in every other page, is measured. After this, the pages are > merged into 2000 pairs and in each pair, 1 page is modified (i.e. they > are decoupled) to detect COW breaks. The time needed to break COW of > merged pages is then compared with performance of non-shared pages. > > The test is run as follows: ./ksm_tests -C > The output: > Total size: 15 MiB > > Not merged pages: > Total time: 0.001903112 s > Average speed: 3678.186 MiB/s > > Merged pages: > Total time: 0.006215680 s > Average speed: 1126.184 MiB/s > > Signed-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@xxxxxxxxx> > --- > v1 -> v2: > As suggested by Pavel, > - add baseline figures with non-shared pages > - instead of having all pages merged together, create pairs of > duplicated pages > > Pavel's review comments: > https://lore.kernel.org/lkml/CA+CK2bDYZBBaU3pC369o01tCgydaJ6y91GZ0_MWONMMCajZOUw@xxxxxxxxxxxxxx/ > > tools/testing/selftests/vm/ksm_tests.c | 84 +++++++++++++++++++++++++- > 1 file changed, 81 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/vm/ksm_tests.c b/tools/testing/selftests/vm/ksm_tests.c > index 432dfe615e50..382ee6ccd13a 100644 > --- a/tools/testing/selftests/vm/ksm_tests.c > +++ b/tools/testing/selftests/vm/ksm_tests.c > @@ -33,7 +33,8 @@ enum ksm_test_name { > CHECK_KSM_UNMERGE, > CHECK_KSM_ZERO_PAGE_MERGE, > CHECK_KSM_NUMA_MERGE, > - KSM_MERGE_TIME > + KSM_MERGE_TIME, > + KSM_COW_TIME > }; > > static int ksm_write_sysfs(const char *file_path, unsigned long val) > @@ -98,7 +99,8 @@ static void print_help(void) > " -U (page unmerging)\n" > " -P evaluate merging time and speed.\n" > " For this test, the size of duplicated memory area (in MiB)\n" > - " must be provided using -s option\n\n"); > + " must be provided using -s option\n" > + " -C evaluate the time required to break COW of merged pages.\n\n"); > > printf(" -a: specify the access protections of pages.\n" > " <prot> must be of the form [rwx].\n" > @@ -455,6 +457,75 @@ static int ksm_merge_time(int mapping, int prot, int timeout, size_t map_size) > return KSFT_FAIL; > } > > +static int ksm_cow_time(int mapping, int prot, int timeout, size_t page_size) > +{ > + void *map_ptr; > + struct timespec start_time, end_time; > + unsigned long cow_time_ns; > + int page_count = 4000; size_t is more correct. > + > + map_ptr = allocate_memory(NULL, prot, mapping, '*', page_size * page_count); > + if (!map_ptr) > + return KSFT_FAIL; > + > + if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) { > + perror("clock_gettime"); > + return KSFT_FAIL; > + } > + for (size_t i = 0; i < page_count; i = i + 2) ^ I think it is best to use the correct test here even though you're stepping by 2 and won't have any problems in practice: i < (page_count - 1) This should be changed in all for loops in this function. > + memset(map_ptr + page_size * i, '-', 1); > + if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) { > + perror("clock_gettime"); > + return KSFT_FAIL; > + } > + > + cow_time_ns = (end_time.tv_sec - start_time.tv_sec) * NSEC_PER_SEC + > + (end_time.tv_nsec - start_time.tv_nsec); > + > + printf("Total size: %lu MiB\n\n", (page_size * page_count) / MB); > + printf("Not merged pages:\n"); > + printf("Total time: %ld.%09ld s\n", cow_time_ns / NSEC_PER_SEC, > + cow_time_ns % NSEC_PER_SEC); > + printf("Average speed: %.3f MiB/s\n\n", ((page_size * (page_count / 2)) / MB) / > + ((double)cow_time_ns / NSEC_PER_SEC)); > + > + /* Create 2000 pairs of duplicated pages */ > + for (size_t i = 0; i < page_count; i = i + 2) { > + memset(map_ptr + page_size * i, '+', i + 1); > + memset(map_ptr + page_size * (i + 1), '+', i + 1); > + } Since i is being used as the third argument to memset(), this loop only works if page_count is less than page_size. I could see someone quickly bumping page_count higher and then unknowingly getting bad test results. Lets gain a little headroom in page_count. We are creating page_count/2 pairs of duplicate pages so we can use these memset() calls: memset(map_ptr + page_size * i, '+', i / 2 + 1); memset(map_ptr + page_size * (i + 1), '+', i / 2 + 1); Then add a short comment to the page_count declaration mentioning that page_count must be < (page_size / 2). Everything else looks good to me. Tyler > + if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout)) > + goto err_out; > + > + if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) { > + perror("clock_gettime"); > + goto err_out; > + } > + for (size_t i = 0; i < page_count; i = i + 2) > + memset(map_ptr + page_size * i, '-', 1); > + if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_time)) { > + perror("clock_gettime"); > + goto err_out; > + } > + > + cow_time_ns = (end_time.tv_sec - start_time.tv_sec) * NSEC_PER_SEC + > + (end_time.tv_nsec - start_time.tv_nsec); > + > + printf("Merged pages:\n"); > + printf("Total time: %ld.%09ld s\n", cow_time_ns / NSEC_PER_SEC, > + cow_time_ns % NSEC_PER_SEC); > + printf("Average speed: %.3f MiB/s\n", ((page_size * (page_count / 2)) / MB) / > + ((double)cow_time_ns / NSEC_PER_SEC)); > + > + munmap(map_ptr, page_size * page_count); > + return KSFT_PASS; > + > +err_out: > + printf("Not OK\n"); > + munmap(map_ptr, page_size * page_count); > + return KSFT_FAIL; > +} > + > int main(int argc, char *argv[]) > { > int ret, opt; > @@ -468,7 +539,7 @@ int main(int argc, char *argv[]) > bool merge_across_nodes = KSM_MERGE_ACROSS_NODES_DEFAULT; > long size_MB = 0; > > - while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNP")) != -1) { > + while ((opt = getopt(argc, argv, "ha:p:l:z:m:s:MUZNPC")) != -1) { > switch (opt) { > case 'a': > prot = str_to_prot(optarg); > @@ -522,6 +593,9 @@ int main(int argc, char *argv[]) > case 'P': > test_name = KSM_MERGE_TIME; > break; > + case 'C': > + test_name = KSM_COW_TIME; > + break; > default: > return KSFT_FAIL; > } > @@ -571,6 +645,10 @@ int main(int argc, char *argv[]) > ret = ksm_merge_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec, > size_MB); > break; > + case KSM_COW_TIME: > + ret = ksm_cow_time(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec, > + page_size); > + break; > } > > if (ksm_restore(&ksm_sysfs_old)) { > -- > 2.25.1 >
