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selftests/mm: mremap_test: optimize execution time from minutes to seconds using chunkwise memcmp

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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.

Link: https://lkml.kernel.org/r/20240330173557.2697684-3-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Dev Jain 2024-03-30 23:05:56 +05:30 committed by Andrew Morton
parent c7876a0cc6
commit 7033c6cc96
1 changed files with 90 additions and 20 deletions
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110
tools/testing/selftests/mm/mremap_test.c
View File

@ -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 @@ out:
/* 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 (((char *) dest_addr)[t] != c) {
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 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 (!c.dest_preamble_size)
goto no_preamble;
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);
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)