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Message-Id: <20240330173557.2697684-3-dev.jain@arm.com>
Date: Sat, 30 Mar 2024 23:05:56 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: shuah@...nel.org,
linux-mm@...ck.org,
linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org,
kaleshsingh@...gle.com,
jhubbard@...dia.com,
Anshuman.Khandual@....com,
Dev Jain <dev.jain@....com>
Subject: [PATCH 2/3] selftests/mm: mremap_test: Optimize execution time from minutes to seconds using chunkwise memcmp
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 <dev.jain@....com>
---
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
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