selftests/damon: add a test for DAMOS apply intervals

Add a selftest for DAMOS apply intervals.  It runs two schemes having
different apply interval agains an artificial memory access workload, and
check if the scheme with smaller apply interval was applied more
frequently.

Link: https://lkml.kernel.org/r/20240207203134.69976-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/Makefile

@@ -12,7 +12,7 @@ TEST_PROGS += debugfs_rm_non_contexts.sh
 TEST_PROGS += sysfs.sh sysfs_update_removed_scheme_dir.sh
 TEST_PROGS += sysfs_update_schemes_tried_regions_hang.py
 TEST_PROGS += sysfs_update_schemes_tried_regions_wss_estimation.py
-TEST_PROGS += damos_quota.py
+TEST_PROGS += damos_quota.py damos_apply_interval.py
 TEST_PROGS += reclaim.sh lru_sort.sh
 
 include ../lib.mk

tools/testing/selftests/damon/damos_apply_interval.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import subprocess
+import time
+
+import _damon_sysfs
+
+def main():
+    # access two 10 MiB memory regions, 2 second per each
+    sz_region = 10 * 1024 * 1024
+    proc = subprocess.Popen(['./access_memory', '2', '%d' % sz_region, '2000'])
+
+    # Set quota up to 1 MiB per 100 ms
+    kdamonds = _damon_sysfs.Kdamonds([_damon_sysfs.Kdamond(
+            contexts=[_damon_sysfs.DamonCtx(
+                ops='vaddr',
+                targets=[_damon_sysfs.DamonTarget(pid=proc.pid)],
+                schemes=[
+                    _damon_sysfs.Damos(
+                        access_pattern=_damon_sysfs.DamosAccessPattern(
+                            # >= 25% access rate, >= 200ms age
+                            nr_accesses=[5, 20], age=[2, 2**64 - 1]),
+                        # aggregation interval (100 ms) is used
+                        apply_interval_us=0),
+                    # use 10ms apply interval
+                    _damon_sysfs.Damos(
+                        access_pattern=_damon_sysfs.DamosAccessPattern(
+                            # >= 25% access rate, >= 200ms age
+                            nr_accesses=[5, 20], age=[2, 2**64 - 1]),
+                        # explicitly set 10 ms apply interval
+                        apply_interval_us=10 * 1000)
+                    ] # schemes
+                )] # contexts
+            )]) # kdamonds
+
+    err = kdamonds.start()
+    if err != None:
+        print('kdamond start failed: %s' % err)
+        exit(1)
+
+    wss_collected = []
+    nr_quota_exceeds = 0
+    while proc.poll() == None:
+        time.sleep(0.1)
+        err = kdamonds.kdamonds[0].update_schemes_stats()
+        if err != None:
+            print('stats update failed: %s' % err)
+            exit(1)
+    schemes = kdamonds.kdamonds[0].contexts[0].schemes
+    nr_tried_stats = [s.stats.nr_tried for s in schemes]
+    if nr_tried_stats[0] == 0 or nr_tried_stats[1] == 0:
+        print('scheme(s) are not tried')
+        exit(1)
+
+    # Because the second scheme was having the apply interval that is ten times
+    # lower than that of the first scheme, the second scheme should be tried
+    # about ten times more frequently than the first scheme.  For possible
+    # timing errors, check if it was at least nine times more freuqnetly tried.
+    ratio = nr_tried_stats[1] / nr_tried_stats[0]
+    if ratio < 9:
+        print('%d / %d = %f (< 9)' %
+              (nr_tried_stats[1], nr_tried_stats[0], ratio))
+        exit(1)
+
+if __name__ == '__main__':
+    main()