This is to slow down lock acquistion (on contention locks) deliberately.
A possible use case is to estimate impact on application performance by
optimization of kernel locking behavior. By delaying the lock it can
simulate the worse condition as a control group, and then compare with
the current behavior as a optimized condition.
The syntax is 'time@function' and the time can have unit suffix like
"us" and "ms". For example, I ran a simple test like below.
$ sudo perf lock con -abl -L tasklist_lock -- \
sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
92 1.18 ms 199.54 us 12.79 us
ffffffff8a806080 tasklist_lock (rwlock)
The contention count was 92 and the average wait time was around 10 us.
But if I add 100 usec of delay to the tasklist_lock,
$ sudo perf lock con -abl -L tasklist_lock -J 100us@tasklist_lock -- \
sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
190 15.67 ms 230.10 us 82.46 us
ffffffff8a806080 tasklist_lock (rwlock)
The contention count increased and the average wait time was up closed
to 100 usec. If I increase the delay even more,
$ sudo perf lock con -abl -L tasklist_lock -J 1ms@tasklist_lock -- \
sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
1002 2.80 s 3.01 ms 2.80 ms
ffffffff8a806080 tasklist_lock (rwlock)
Now every sleep process had contention and the wait time was more than 1
msec. This is on my 4 CPU laptop so I guess one CPU has the lock while
other 3 are waiting for it mostly.
For simplicity, it only supports global locks for now.
Committer testing:
root@number:~# grep -m1 'model name' /proc/cpuinfo
model name : AMD Ryzen 9 9950X3D 16-Core Processor
root@number:~# perf lock con -abl -L tasklist_lock -- sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
142 453.85 us 25.39 us 3.20 us
ffffffffae808080 tasklist_lock (rwlock)
root@number:~# perf lock con -abl -L tasklist_lock -J 100us@tasklist_lock -- sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
1040 2.39 s 3.11 ms 2.30 ms
ffffffffae808080 tasklist_lock (rwlock)
root@number:~# perf lock con -abl -L tasklist_lock -J 1ms@tasklist_lock -- sh -c 'for i in $(seq 1000); do sleep 1 & done; wait'
contended total wait max wait avg wait address symbol
1025 24.72 s 31.01 ms 24.12 ms
ffffffffae808080 tasklist_lock (rwlock)
root@number:~#
Suggested-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250509171950.183591-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
--cgroup-filter=<value>::
Show lock contention only in the given cgroups (comma separated list).
+-J::
+--inject-delay=<time@function>::
+ Add delays to the given lock. It's added to the contention-end part so
+ that the (new) owner of the lock will be delayed. But by slowing down
+ the owner, the waiters will also be delayed as well. This is working
+ only with -b/--use-bpf.
+
+ The 'time' is specified in nsec but it can have a unit suffix. Available
+ units are "ms" and "us". Note that it will busy-wait after it gets the
+ lock. Please use it at your own risk.
+
SEE ALSO
--------
static FILE *lock_output;
static struct lock_filter filters;
+static struct lock_delay *delays;
+static int nr_delays;
static enum lock_aggr_mode aggr_mode = LOCK_AGGR_ADDR;
.max_stack = max_stack_depth,
.stack_skip = stack_skip,
.filters = &filters,
+ .delays = delays,
+ .nr_delays = nr_delays,
.save_callstack = needs_callstack(),
.owner = show_lock_owner,
.cgroups = RB_ROOT,
return ret;
}
+static bool add_lock_delay(char *spec)
+{
+ char *at, *pos;
+ struct lock_delay *tmp;
+ unsigned long duration;
+
+ at = strchr(spec, '@');
+ if (at == NULL) {
+ pr_err("lock delay should have '@' sign: %s\n", spec);
+ return false;
+ }
+ if (at == spec) {
+ pr_err("lock delay should have time before '@': %s\n", spec);
+ return false;
+ }
+
+ *at = '\0';
+ duration = strtoul(spec, &pos, 0);
+ if (!strcmp(pos, "ns"))
+ duration *= 1;
+ else if (!strcmp(pos, "us"))
+ duration *= 1000;
+ else if (!strcmp(pos, "ms"))
+ duration *= 1000 * 1000;
+ else if (*pos) {
+ pr_err("invalid delay time: %s@%s\n", spec, at + 1);
+ return false;
+ }
+
+ tmp = realloc(delays, (nr_delays + 1) * sizeof(*delays));
+ if (tmp == NULL) {
+ pr_err("Memory allocation failure\n");
+ return false;
+ }
+ delays = tmp;
+
+ delays[nr_delays].sym = strdup(at + 1);
+ if (delays[nr_delays].sym == NULL) {
+ pr_err("Memory allocation failure\n");
+ return false;
+ }
+ delays[nr_delays].time = duration;
+
+ nr_delays++;
+ return true;
+}
+
+static int parse_lock_delay(const struct option *opt __maybe_unused, const char *str,
+ int unset __maybe_unused)
+{
+ char *s, *tmp, *tok;
+ int ret = 0;
+
+ s = strdup(str);
+ if (s == NULL)
+ return -1;
+
+ for (tok = strtok_r(s, ", ", &tmp); tok; tok = strtok_r(NULL, ", ", &tmp)) {
+ if (!add_lock_delay(tok)) {
+ ret = -1;
+ break;
+ }
+ }
+
+ free(s);
+ return ret;
+}
+
int cmd_lock(int argc, const char **argv)
{
const struct option lock_options[] = {
OPT_BOOLEAN(0, "lock-cgroup", &show_lock_cgroups, "show lock stats by cgroup"),
OPT_CALLBACK('G', "cgroup-filter", NULL, "CGROUPS",
"Filter specific cgroups", parse_cgroup_filter),
+ OPT_CALLBACK('J', "inject-delay", NULL, "TIME@FUNC",
+ "Inject delays to specific locks", parse_lock_delay),
OPT_PARENT(lock_options)
};
skel->rodata->has_addr = 1;
}
+ /* resolve lock name in delays */
+ if (con->nr_delays) {
+ struct symbol *sym;
+ struct map *kmap;
+
+ for (i = 0; i < con->nr_delays; i++) {
+ sym = machine__find_kernel_symbol_by_name(con->machine,
+ con->delays[i].sym,
+ &kmap);
+ if (sym == NULL) {
+ pr_warning("ignore unknown symbol: %s\n",
+ con->delays[i].sym);
+ continue;
+ }
+
+ con->delays[i].addr = map__unmap_ip(kmap, sym->start);
+ }
+ skel->rodata->lock_delay = 1;
+ bpf_map__set_max_entries(skel->maps.lock_delays, con->nr_delays);
+ }
+
bpf_map__set_max_entries(skel->maps.cpu_filter, ncpus);
bpf_map__set_max_entries(skel->maps.task_filter, ntasks);
bpf_map__set_max_entries(skel->maps.type_filter, ntypes);
bpf_map_update_elem(fd, &con->filters->cgrps[i], &val, BPF_ANY);
}
+ if (con->nr_delays) {
+ fd = bpf_map__fd(skel->maps.lock_delays);
+
+ for (i = 0; i < con->nr_delays; i++)
+ bpf_map_update_elem(fd, &con->delays[i].addr, &con->delays[i].time, BPF_ANY);
+ }
+
if (con->aggr_mode == LOCK_AGGR_CGROUP)
read_all_cgroups(&con->cgroups);
/* for collect_zone_lock(). It should be more than the actual zones. */
#define MAX_ZONES 10
+/* for do_lock_delay(). Arbitrarily set to 1 million. */
+#define MAX_LOOP (1U << 20)
+
/* lock contention flags from include/trace/events/lock.h */
#define LCB_F_SPIN (1U << 0)
#define LCB_F_READ (1U << 1)
__uint(max_entries, 1);
} slab_caches SEC(".maps");
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(key_size, sizeof(__u64));
+ __uint(value_size, sizeof(__u64));
+ __uint(max_entries, 1);
+} lock_delays SEC(".maps");
+
struct rw_semaphore___old {
struct task_struct *owner;
} __attribute__((preserve_access_index));
const volatile int lock_owner;
const volatile int use_cgroup_v2;
const volatile int max_stack;
+const volatile int lock_delay;
/* determine the key of lock stat */
const volatile int aggr_mode;
return 0;
}
+static inline long delay_callback(__u64 idx, void *arg)
+{
+ __u64 target = *(__u64 *)arg;
+
+ if (target <= bpf_ktime_get_ns())
+ return 1;
+
+ /* just to kill time */
+ (void)bpf_get_prandom_u32();
+
+ return 0;
+}
+
+static inline void do_lock_delay(__u64 duration)
+{
+ __u64 target = bpf_ktime_get_ns() + duration;
+
+ bpf_loop(MAX_LOOP, delay_callback, &target, /*flags=*/0);
+}
+
+static inline void check_lock_delay(__u64 lock)
+{
+ __u64 *delay;
+
+ delay = bpf_map_lookup_elem(&lock_delays, &lock);
+ if (delay)
+ do_lock_delay(*delay);
+}
+
static inline struct tstamp_data *get_tstamp_elem(__u32 flags)
{
__u32 pid;
update_contention_data(data, duration, 1);
out:
+ if (lock_delay)
+ check_lock_delay(pelem->lock);
+
pelem->lock = 0;
if (need_delete)
bpf_map_delete_elem(&tstamp, &pid);
char **slabs;
};
+struct lock_delay {
+ char *sym;
+ unsigned long addr;
+ unsigned long time;
+};
+
struct lock_stat {
struct hlist_node hash_entry;
struct rb_node rb; /* used for sorting */
struct machine *machine;
struct hlist_head *result;
struct lock_filter *filters;
+ struct lock_delay *delays;
struct lock_contention_fails fails;
struct rb_root cgroups;
void *btf;
int aggr_mode;
int owner;
int nr_filtered;
+ int nr_delays;
bool save_callstack;
};
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