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perf lock contention: Enable end-timestamp accounting for cgroup aggregation

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update_lock_stat() handles lock contentions that start but never reach a
contention_end event (e.g., locks still held when profiling stops), but
previously treated LOCK_AGGR_CGROUP as a no-op due to missing cgroup
context in userspace.

Fix this by adding a cgroup_id field to struct tstamp_data, recording it
at contention_begin using get_current_cgroup_id() when aggr_mode is
LOCK_AGGR_CGROUP. Capturing it at contention_begin is semantically
correct, the contention cost is incurred by the task that had to wait,
not by whatever task happens to be running at contention_end. It is also
preferable from a performance standpoint, as contention_end runs just
before the task enters the critical section.

Update contention_end to use pelem->cgroup_id instead of calling
get_current_cgroup_id() dynamically, ensuring both complete and
incomplete contention events attribute the wait time to the cgroup at
wait-start time consistently.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Suchit Karunakaran <suchitkarunakaran@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tycho Andersen (AMD) <tycho@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Suchit Karunakaran
2026-05-31 01:29:40 +05:30
committed by Arnaldo Carvalho de Melo
parent be694c488a
commit 824b18f607
3 changed files with 6 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
tools/perf/util/bpf_lock_contention.c
View File

@@ -470,8 +470,8 @@ static void update_lock_stat(int map_fd, int pid, u64 end_ts,
stat_key.lock_addr_or_cgroup = ts_data->lock;
break;
case LOCK_AGGR_CGROUP:
/* TODO */
return;
stat_key.lock_addr_or_cgroup = ts_data->cgroup_id;
break;
default:
return;
}

4
tools/perf/util/bpf_skel/lock_contention.bpf.c
View File

@@ -597,6 +597,8 @@ int contention_begin(u64 *ctx)
pelem->timestamp = bpf_ktime_get_ns();
pelem->lock = (__u64)ctx[0];
pelem->flags = (__u32)ctx[1];
if (aggr_mode == LOCK_AGGR_CGROUP)
pelem->cgroup_id = get_current_cgroup_id();
if (needs_callstack) {
u32 i = 0;
@@ -832,7 +834,7 @@ int contention_end(u64 *ctx)
key.stack_id = pelem->stack_id;
break;
case LOCK_AGGR_CGROUP:
key.lock_addr_or_cgroup = get_current_cgroup_id();
key.lock_addr_or_cgroup = pelem->cgroup_id;
break;
default:
/* should not happen */

1
tools/perf/util/bpf_skel/lock_data.h
View File

@@ -13,6 +13,7 @@ struct owner_tracing_data {
struct tstamp_data {
u64 timestamp;
u64 lock;
u64 cgroup_id;
u32 flags;
s32 stack_id;
};