* [PATCH] trace_branch: use per-cpu counters for correct/incorrect stats
@ 2026-06-29 9:58 Martin Weiss
2026-06-29 10:47 ` Steven Rostedt
0 siblings, 1 reply; 2+ messages in thread
From: Martin Weiss @ 2026-06-29 9:58 UTC (permalink / raw)
To: linux-kernel
Cc: Martin Weiss, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
Replace per-task counters with per-cpu increments to avoid race
conditions in the branch profiler fast path.
Fixes FIXME about atomicity.
Signed-off-by: Martin Weiss <Martin.weiss2410@gmail.com>
---
kernel/trace/trace_branch.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index d8e97ad798f0..960bcb3d7dbf 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -213,11 +213,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
*/
trace_likely_condition(f, val, expect);
- /* FIXME: Make this atomic! */
+ /* use per-cpu counters to avoid contention */
if (val == expect)
- f->data.correct++;
+ this_cpu_inc(f->data.correct);
else
- f->data.incorrect++;
+ this_cpu_inc(f->data.incorrect);
user_access_restore(flags);
}
--
2.54.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] trace_branch: use per-cpu counters for correct/incorrect stats
2026-06-29 9:58 [PATCH] trace_branch: use per-cpu counters for correct/incorrect stats Martin Weiss
@ 2026-06-29 10:47 ` Steven Rostedt
0 siblings, 0 replies; 2+ messages in thread
From: Steven Rostedt @ 2026-06-29 10:47 UTC (permalink / raw)
To: Martin Weiss
Cc: linux-kernel, Martin Weiss, Masami Hiramatsu, Mathieu Desnoyers,
linux-trace-kernel
On Mon, 29 Jun 2026 16:58:38 +0700
Martin Weiss <martin.githubacc@gmail.com> wrote:
> Replace per-task counters with per-cpu increments to avoid race
> conditions in the branch profiler fast path.
>
> Fixes FIXME about atomicity.
>
> Signed-off-by: Martin Weiss <Martin.weiss2410@gmail.com>
> ---
> kernel/trace/trace_branch.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index d8e97ad798f0..960bcb3d7dbf 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -213,11 +213,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> */
> trace_likely_condition(f, val, expect);
>
> - /* FIXME: Make this atomic! */
> + /* use per-cpu counters to avoid contention */
> if (val == expect)
> - f->data.correct++;
> + this_cpu_inc(f->data.correct);
> else
> - f->data.incorrect++;
> + this_cpu_inc(f->data.incorrect);
I don't think this does what you think it does.
Did you even test this? I'm guessing it would blow up in some fantastic
ways.
NAK.
-- Steve
>
> user_access_restore(flags);
> }
^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-06-29 9:58 [PATCH] trace_branch: use per-cpu counters for correct/incorrect stats Martin Weiss
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