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/sSigned-off-by: Zhansaya Bagdauletkyzy zhansayabagdaulet@gmail.com
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_MWONMMCaj...
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;@@ -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