linux-kernel - Re: [POC][RFC][PATCH 1/3] tracing: Add perf events

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Message-ID: <20251118152425.6b3bee21@gandalf.local.home>
Date: Tue, 18 Nov 2025 15:24:25 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Ian
 Rogers <irogers@...gle.com>, Namhyung Kim <namhyung@...nel.org>, Arnaldo
 Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Douglas
 Raillard <douglas.raillard@....com>
Subject: Re: [POC][RFC][PATCH 1/3] tracing: Add perf events

On Tue, 18 Nov 2025 08:42:26 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> > 
> > What you wanted to use was perf_event_read_local().  
> 
> Great! I didn't know about that. Which is why I posted this as a
> PROOF-OF-CONCEPT and not even a normal RFC, so that I could learn about the
> proper way of doing this.

I folded in this change:

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index ff864d300251..34962f80dce1 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -478,6 +478,7 @@ u64 do_trace_perf_event(int type)
 	struct trace_perf_event __percpu **pevents;
 	struct trace_perf_event __percpu *events;
 	struct perf_event *e;
+	u64 val;
 	int *count;
 	int cpu;
 
@@ -499,8 +500,10 @@ u64 do_trace_perf_event(int type)
 	if (!e)
 		return 0;
 
-	e->pmu->read(e);
-	return local64_read(&e->count);
+	if (perf_event_read_local(e, &val, NULL, NULL) < 0)
+		return 0;
+
+	return val;
 }
 
 static void __free_trace_perf_events(struct trace_perf_event __percpu *events)

Thanks!

-- Steve