From 311ead1be05d2348e89f873337c8375e856e1abb Mon Sep 17 00:00:00 2001 From: Guopeng Zhang Date: Wed, 3 Dec 2025 19:56:29 +0800 Subject: [PATCH] selftests: cgroup: Add cg_read_key_long_poll() to poll a cgroup key with retries MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Introduce a new helper function `cg_read_key_long_poll()` in cgroup_util.h. This function polls the specified key in a cgroup file until it matches the expected value or the retry limit is reached, with configurable wait intervals between retries. This helper is particularly useful for handling asynchronously updated cgroup statistics (e.g., memory.stat), where immediate reads may observe stale values, especially on busy systems. It allows tests and other utilities to handle such cases more flexibly. Signed-off-by: Guopeng Zhang Suggested-by: Michal Koutný Reviewed-by: Shakeel Butt Acked-by: Michal Koutný Signed-off-by: Tejun Heo --- .../selftests/cgroup/lib/cgroup_util.c | 21 +++++++++++++++++++ .../cgroup/lib/include/cgroup_util.h | 5 +++++ 2 files changed, 26 insertions(+) diff --git a/tools/testing/selftests/cgroup/lib/cgroup_util.c b/tools/testing/selftests/cgroup/lib/cgroup_util.c index 44c52f620fda1..ce6c2642fd9bb 100644 --- a/tools/testing/selftests/cgroup/lib/cgroup_util.c +++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c @@ -168,6 +168,27 @@ long cg_read_key_long(const char *cgroup, const char *control, const char *key) return atol(ptr + strlen(key)); } +long cg_read_key_long_poll(const char *cgroup, const char *control, + const char *key, long expected, int retries, + useconds_t wait_interval_us) +{ + long val = -1; + int i; + + for (i = 0; i < retries; i++) { + val = cg_read_key_long(cgroup, control, key); + if (val < 0) + return val; + + if (val == expected) + break; + + usleep(wait_interval_us); + } + + return val; +} + long cg_read_lc(const char *cgroup, const char *control) { char buf[PAGE_SIZE]; diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h index 7ab2824ed7b54..77f386dab5e8f 100644 --- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h @@ -17,6 +17,8 @@ #define CG_NAMED_NAME "selftest" #define CG_PATH_FORMAT (!cg_test_v1_named ? "0::%s" : (":name=" CG_NAMED_NAME ":%s")) +#define DEFAULT_WAIT_INTERVAL_US (100 * 1000) /* 100 ms */ + /* * Checks if two given values differ by less than err% of their sum. */ @@ -64,6 +66,9 @@ extern int cg_read_strstr(const char *cgroup, const char *control, extern long cg_read_long(const char *cgroup, const char *control); extern long cg_read_long_fd(int fd); long cg_read_key_long(const char *cgroup, const char *control, const char *key); +long cg_read_key_long_poll(const char *cgroup, const char *control, + const char *key, long expected, int retries, + useconds_t wait_interval_us); extern long cg_read_lc(const char *cgroup, const char *control); extern int cg_write(const char *cgroup, const char *control, char *buf); extern int cg_open(const char *cgroup, const char *control, int flags); -- 2.47.3