linux-kernel - [PATCH 6/7] perf lock contention: Revise needs

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Date:   Thu,  6 Apr 2023 14:06:10 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, Song Liu <song@...nel.org>,
        Hao Luo <haoluo@...gle.com>, bpf@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH 6/7] perf lock contention: Revise needs_callstack() condition

It needs callstacks for two reasons:

 * for stack aggregation mode, the map key is the stack id and it can
   also show the full stack traces when -v is used

 * for other aggregation modes, the stack filter can be used to limit
   lock contentions from known call paths

The -v option is meaningful (in terms of stack trace) only for stack
aggregation mode, so it should not set the save_callstack for other
mode like with -t or -l options.

I've noticed this with the following command line:

  $ sudo ./perf lock con -ablv -E 3 -M 16 -- ./perf bench sched messaging
  ...
   contended   total wait     max wait     avg wait            address   symbol

          88      4.59 ms    108.07 us     52.13 us   ffff935757f46ec0    (spinlock)
          33    905.22 us     73.67 us     27.43 us   ffff935757f41700    (spinlock)
          28    703.69 us     79.28 us     25.13 us   ffff938a3d9b0c80   rq_lock (spinlock)

  === output for debug ===

  bad: 12272, total: 12421
  bad rate: 98.80 %
  histogram of failure reasons
         task: 8285
        stack: 3987    <---------- here
         time: 0
         data: 0

It should not have any failure on stacks since it doesn't use it.
No functional change intended.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/builtin-lock.c             | 2 +-
 tools/perf/util/bpf_lock_contention.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 7742fa255c44..4e24351b18bd 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -77,7 +77,7 @@ static enum lock_aggr_mode aggr_mode = LOCK_AGGR_ADDR;
 
 static bool needs_callstack(void)
 {
-	return verbose > 0 || !list_empty(&callstack_filters);
+	return !list_empty(&callstack_filters);
 }
 
 static struct thread_stat *thread_stat_find(u32 tid)
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index ea4f697d2a9f..9e20fa8ade09 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -346,7 +346,7 @@ int lock_contention_read(struct lock_contention *con)
 		if (data.count)
 			st->avg_wait_time = data.total_time / data.count;
 
-		if (con->save_callstack) {
+		if (con->aggr_mode == LOCK_AGGR_CALLER && verbose > 0) {
 			st->callstack = memdup(stack_trace, stack_size);
 			if (st->callstack == NULL)
 				break;
-- 
2.40.0.577.gac1e443424-goog