Mismatch index is currently being checked by a brute force iteration over the buffer. Instead, break the comparison into O(sqrt(n)) number of chunks, with the chunk size of this order only, where n is the size of the buffer. Do a brute-force iteration to print to stdout only when the highly optimized memcmp() library function returns a mismatch in the chunk. The time complexity of this algorithm is O(sqrt(n)) * t, where t is the time taken by memcmp(); for our test conditions, it is safe to assume t to be small.
NOTE: This patch depends on the previous one. Signed-off-by: Dev Jain <[email protected]> --- tools/testing/selftests/mm/mremap_test.c | 112 ++++++++++++++++++----- 1 file changed, 91 insertions(+), 21 deletions(-) diff --git a/tools/testing/selftests/mm/mremap_test.c b/tools/testing/selftests/mm/mremap_test.c index 7fed9cc3911e..678c79d5b8ef 100644 --- a/tools/testing/selftests/mm/mremap_test.c +++ b/tools/testing/selftests/mm/mremap_test.c @@ -70,6 +70,27 @@ enum { .expect_failure = should_fail \ } +/* compute square root using binary search */ +static unsigned long get_sqrt(unsigned long val) +{ + unsigned long low = 1; + + /* assuming rand_size is less than 1TB */ + unsigned long high = (1UL << 20); + + while (low <= high) { + unsigned long mid = low + (high - low) / 2; + unsigned long temp = mid * mid; + + if (temp == val) + return mid; + if (temp < val) + low = mid + 1; + high = mid - 1; + } + return low; +} + /* * Returns false if the requested remap region overlaps with an * existing mapping (e.g text, stack) else returns true. @@ -355,14 +376,14 @@ static void mremap_move_within_range(unsigned int pattern_seed, char *rand_addr) /* Returns the time taken for the remap on success else returns -1. */ static long long remap_region(struct config c, unsigned int threshold_mb, - unsigned int pattern_seed, char *rand_addr) + char *rand_addr) { void *addr, *src_addr, *dest_addr, *dest_preamble_addr; - int d; - unsigned long long t; + unsigned long long t, d; struct timespec t_start = {0, 0}, t_end = {0, 0}; long long start_ns, end_ns, align_mask, ret, offset; unsigned long long threshold; + unsigned long num_chunks; if (threshold_mb == VALIDATION_NO_THRESHOLD) threshold = c.region_size; @@ -430,15 +451,42 @@ static long long remap_region(struct config c, unsigned int threshold_mb, goto clean_up_dest_preamble; } - /* Verify byte pattern after remapping */ - srand(pattern_seed); - for (t = 0; t < threshold; t++) { - char c = (char) rand(); + /* + * Verify byte pattern after remapping. Employ an algorithm with a + * square root time complexity in threshold: divide the range into + * chunks, if memcmp() returns non-zero, only then perform an + * iteration in that chunk to find the mismatch index. + */ + num_chunks = get_sqrt(threshold); + for (unsigned long i = 0; i < num_chunks; ++i) { + size_t chunk_size = threshold / num_chunks; + unsigned long shift = i * chunk_size; + + if (!memcmp(dest_addr + shift, rand_addr + shift, chunk_size)) + continue; + + /* brute force iteration only over mismatch segment */ + for (t = shift; t < shift + chunk_size; ++t) { + if (((char *) dest_addr)[t] != rand_addr[t]) { + ksft_print_msg("Data after remap doesn't match at offset %llu\n", + t); + ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[t] & 0xff, + ((char *) dest_addr)[t] & 0xff); + ret = -1; + goto clean_up_dest; + } + } + } - if (((char *) dest_addr)[t] != c) { + /* + * if threshold is not divisible by num_chunks, then check the + * last chunk + */ + for (t = num_chunks * (threshold / num_chunks); t < threshold; ++t) { + if (((char *) dest_addr)[t] != rand_addr[t]) { ksft_print_msg("Data after remap doesn't match at offset %llu\n", - t); - ksft_print_msg("Expected: %#x\t Got: %#x\n", c & 0xff, + t); + ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[t] & 0xff, ((char *) dest_addr)[t] & 0xff); ret = -1; goto clean_up_dest; @@ -446,22 +494,44 @@ static long long remap_region(struct config c, unsigned int threshold_mb, } /* Verify the dest preamble byte pattern after remapping */ - if (c.dest_preamble_size) { - srand(pattern_seed); - for (d = 0; d < c.dest_preamble_size; d++) { - char c = (char) rand(); - - if (((char *) dest_preamble_addr)[d] != c) { - ksft_print_msg("Preamble data after remap doesn't match at offset %d\n", - d); - ksft_print_msg("Expected: %#x\t Got: %#x\n", c & 0xff, - ((char *) dest_preamble_addr)[d] & 0xff); + if (!c.dest_preamble_size) + goto no_preamble; + + num_chunks = get_sqrt(c.dest_preamble_size); + + for (unsigned long i = 0; i < num_chunks; ++i) { + size_t chunk_size = c.dest_preamble_size / num_chunks; + unsigned long shift = i * chunk_size; + + if (!memcmp(dest_preamble_addr + shift, rand_addr + shift, + chunk_size)) + continue; + + /* brute force iteration only over mismatched segment */ + for (d = shift; d < shift + chunk_size; ++d) { + if (((char *) dest_preamble_addr)[d] != rand_addr[d]) { + ksft_print_msg("Preamble data after remap doesn't match at offset %llu\n", + d); + ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[d] & 0xff, + ((char *) dest_preamble_addr)[d] & 0xff); ret = -1; goto clean_up_dest; } } } + for (d = num_chunks * (c.dest_preamble_size / num_chunks); d < c.dest_preamble_size; ++d) { + if (((char *) dest_preamble_addr)[d] != rand_addr[d]) { + ksft_print_msg("Preamble data after remap doesn't match at offset %llu\n", + d); + ksft_print_msg("Expected: %#x\t Got: %#x\n", rand_addr[d] & 0xff, + ((char *) dest_preamble_addr)[d] & 0xff); + ret = -1; + goto clean_up_dest; + } + } + +no_preamble: start_ns = t_start.tv_sec * NS_PER_SEC + t_start.tv_nsec; end_ns = t_end.tv_sec * NS_PER_SEC + t_end.tv_nsec; ret = end_ns - start_ns; @@ -563,7 +633,7 @@ static void run_mremap_test_case(struct test test_case, int *failures, unsigned int pattern_seed, char *rand_addr) { long long remap_time = remap_region(test_case.config, threshold_mb, - pattern_seed, rand_addr); + rand_addr); if (remap_time < 0) { if (test_case.expect_failure) -- 2.34.1
