[RFC PATCH 4/5] selftests/damon: add a test for update_schemes_tried_regions sysfs command

[SeongJae Park <sj@kernel.org>]

Add a basic test for verifying accuracy of DAMON's access monitoring
functionality.  The test starts a program of artificial access pattern,
monitor the accesses using DAMON, and check if DAMON gets working set
size with reasonable amount of error rate.  Note that the acceptable
error rate is set with only a naive assumption.  Failure of this test
may not always mean DAMON is broken, and we could adjust it in future.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/Makefile        |  2 +
 tools/testing/selftests/damon/access_memory.c | 41 ++++++++++++++++
 ...te_schemes_tried_regions_wss_estimation.py | 48 +++++++++++++++++++
 3 files changed, 91 insertions(+)
 create mode 100644 tools/testing/selftests/damon/access_memory.c
 create mode 100755 tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py

diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
index d2105d41ea25..1363987709c6 100644
--- a/tools/testing/selftests/damon/Makefile
+++ b/tools/testing/selftests/damon/Makefile
@@ -4,6 +4,7 @@
 TEST_GEN_FILES += huge_count_read_write
 TEST_GEN_FILES += dbgfs_target_ids_read_before_terminate_race
 TEST_GEN_FILES += dbgfs_target_ids_pid_leak
+TEST_GEN_FILES += access_memory
 
 TEST_FILES = _chk_dependency.sh _debugfs_common.sh
 TEST_PROGS = debugfs_attrs.sh debugfs_schemes.sh debugfs_target_ids.sh
@@ -11,6 +12,7 @@ TEST_PROGS += debugfs_empty_targets.sh debugfs_huge_count_read_write.sh
 TEST_PROGS += debugfs_duplicate_context_creation.sh
 TEST_PROGS += debugfs_rm_non_contexts.sh
 TEST_PROGS += sysfs.sh sysfs_update_removed_scheme_dir.sh
+TEST_PROGS += sysfs_update_schemes_tried_regions_wss_estimation.py
 TEST_PROGS += reclaim.sh lru_sort.sh
 TEST_PROGS += dbgfs_target_ids_read_before_terminate_race.sh
 TEST_PROGS += dbgfs_target_ids_pid_leak.sh
diff --git a/tools/testing/selftests/damon/access_memory.c b/tools/testing/selftests/damon/access_memory.c
new file mode 100644
index 000000000000..585a2fa54329
--- /dev/null
+++ b/tools/testing/selftests/damon/access_memory.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Artificial memory access program for testing DAMON.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+int main(int argc, char *argv[])
+{
+	char **regions;
+	clock_t start_clock;
+	int nr_regions;
+	int sz_region;
+	int access_time_ms;
+	int i;
+
+	if (argc != 4) {
+		printf("Usage: %s <number> <size (bytes)> <time (ms)>\n",
+				argv[0]);
+		return -1;
+	}
+
+	nr_regions = atoi(argv[1]);
+	sz_region = atoi(argv[2]);
+	access_time_ms = atoi(argv[3]);
+
+	regions = malloc(sizeof(*regions) * nr_regions);
+	for (i = 0; i < nr_regions; i++)
+		regions[i] = malloc(sz_region);
+
+	for (i = 0; i < nr_regions; i++) {
+		start_clock = clock();
+		while ((clock() - start_clock) * 1000 / CLOCKS_PER_SEC <
+				access_time_ms)
+			memset(regions[i], i, 1024 * 1024 * 10);
+	}
+	return 0;
+}
diff --git a/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py b/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py
new file mode 100755
index 000000000000..2aa66f4ad2dc
--- /dev/null
+++ b/tools/testing/selftests/damon/sysfs_update_schemes_tried_regions_wss_estimation.py
@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import subprocess
+import time
+
+import _damon
+
+def main():
+    # access three 10 MiB memory regions, 1 second per each
+    sz_region = 10 * 1024 * 1024
+    proc = subprocess.Popen(['./access_memory', '3', '%d' % sz_region, '1000'])
+    kdamonds = _damon.Kdamonds([_damon.Kdamond(
+            contexts=[_damon.DamonCtx(
+                ops='vaddr',
+                targets=[_damon.DamonTarget(pid=proc.pid)],
+                schemes=[_damon.Damos(
+                    access_pattern=_damon.DamosAccessPattern(
+                        nr_accesses=[1, 20]))] # schemes
+                )] # contexts
+            )]) # kdamonds
+
+    err = kdamonds.start()
+    if err != None:
+        print('kdmaond start failed: %s' % err)
+        exit(1)
+
+    wss_collected = []
+    while proc.poll() == None:
+        time.sleep(0.1)
+        err = kdamonds.kdamonds[0].update_schemes_tried_bytes()
+        if err != None:
+            print('tried bytes update failed: %s' % err)
+            exit(1)
+
+        wss_collected.append(
+                kdamonds.kdamonds[0].contexts[0].schemes[0].tried_bytes)
+
+    wss_collected.sort()
+    for percentile in [25, 75]:
+        sample = wss_collected[int(len(wss_collected) * percentile / 100)]
+        error_rate = abs(sample - sz_region) / sz_region
+        print('%d-th percentile error %f' % (percentile, error_rate))
+        if error_rate > 0.5:
+            exit(1)
+
+if __name__ == '__main__':
+    main()
-- 
2.34.1