linux-kernel - Re: [PATCH v4 09/10] perf stat: Read tool events last

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Message-ID: <aRvbZbhcsjpCXiAU@google.com>
Date: Mon, 17 Nov 2025 18:35:17 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Yang Li <yang.lee@...ux.alibaba.com>,
	James Clark <james.clark@...aro.org>,
	Thomas Falcon <thomas.falcon@...el.com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v4 09/10] perf stat: Read tool events last

On Thu, Nov 13, 2025 at 10:05:15AM -0800, Ian Rogers wrote:
> When reading a metric like memory bandwidth on multiple sockets, the
> additional sockets will be on CPUS > 0. Because of the affinity
> reading, the counters are read on CPU 0 along with the time, then the
> later sockets are read. This can lead to the later sockets having a
> bandwidth larger than is possible for the period of time. To avoid
> this moving the reading of tool events to occur after all other events
> are read.

Can you move this change before the affinity updates?  I think it's
straight-forward and can be applied independently.

Thanks,
Namhyung

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/builtin-stat.c | 29 ++++++++++++++++++++++++++++-
>  tools/perf/util/evlist.c  |  4 ----
>  2 files changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 947f11b8b106..aec93b91fd11 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -379,6 +379,9 @@ static int read_counters_with_affinity(void)
>  		if (evsel__is_bpf(counter))
>  			continue;
>  
> +		if (evsel__is_tool(counter))
> +			continue;
> +
>  		if (!counter->err)
>  			counter->err = read_counter_cpu(counter, evlist_cpu_itr.cpu_map_idx);
>  	}
> @@ -402,6 +405,24 @@ static int read_bpf_map_counters(void)
>  	return 0;
>  }
>  
> +static int read_tool_counters(void)
> +{
> +	struct evsel *counter;
> +
> +	evlist__for_each_entry(evsel_list, counter) {
> +		int idx;
> +
> +		if (!evsel__is_tool(counter))
> +			continue;
> +
> +		perf_cpu_map__for_each_idx(idx, counter->core.cpus) {
> +			if (!counter->err)
> +				counter->err = read_counter_cpu(counter, idx);
> +		}
> +	}
> +	return 0;
> +}
> +
>  static int read_counters(void)
>  {
>  	int ret;
> @@ -415,7 +436,13 @@ static int read_counters(void)
>  		return ret;
>  
>  	// Read non-BPF and non-tool counters next.
> -	return read_counters_with_affinity();
> +	ret = read_counters_with_affinity();
> +	if (ret)
> +		return ret;
> +
> +	// Read the tool counters last. This way the duration_time counter
> +	// should always be greater than any other counter's enabled time.
> +	return read_tool_counters();
>  }
>  
>  static void process_counters(void)
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index b6df81b8a236..fc3dae7cdfca 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -368,10 +368,6 @@ static bool evlist__use_affinity(struct evlist *evlist)
>  	struct perf_cpu_map *used_cpus = NULL;
>  	bool ret = false;
>  
> -	/*
> -	 * With perf record core.user_requested_cpus is usually NULL.
> -	 * Use the old method to handle this for now.
> -	 */
>  	if (!evlist->core.user_requested_cpus ||
>  	    cpu_map__is_dummy(evlist->core.user_requested_cpus))
>  		return false;
> -- 
> 2.51.2.1041.gc1ab5b90ca-goog
>