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

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Message-ID: <20251118083510.GI3245006@noisy.programming.kicks-ass.net>
Date: Tue, 18 Nov 2025 09:35:10 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...nel.org>
Cc: 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 Mon, Nov 17, 2025 at 07:29:51PM -0500, Steven Rostedt wrote:
> +u64 do_trace_perf_event(int type)
> +{
> +	struct trace_perf_event __percpu **pevents;
> +	struct trace_perf_event __percpu *events;
> +	struct perf_event *e;
> +	int *count;
> +	int cpu;
> +
> +	if (set_perf_type(type, NULL, NULL, &count, &pevents) < 0)
> +		return 0;
> +
> +	if (!*count)
> +		return 0;
> +
> +	guard(preempt)();
> +
> +	events = READ_ONCE(*pevents);
> +	if (!events)
> +		return 0;
> +
> +	cpu = smp_processor_id();
> +
> +	e = per_cpu_ptr(events, cpu)->event;
> +	if (!e)
> +		return 0;
> +
> +	e->pmu->read(e);
> +	return local64_read(&e->count);
> +}

NAK, wtf do you think its okay to use internal stuff like that? And
wrongly while at it.

What you wanted to use was perf_event_read_local().