linux-kernel - Re: [PATCH 2/3] perf/core: Set data->sample_flags in perf_prepare

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Message-ID: <Y71ELS9GTz0hqaUt@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Jan 2023 11:55:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@....com>, bpf@...r.kernel.org
Subject: Re: [PATCH 2/3] perf/core: Set data->sample_flags in
 perf_prepare_sample()

On Mon, Jan 09, 2023 at 12:21:25PM -0800, Namhyung Kim wrote:

> > However; inspired by your next patch; we can do something like so:
> > 
> > 	if (filtered_sample_type & PERF_SAMPLE_CALLCHAIN) {
> > 		data->callchain = perf_callchain(event, regs);
> > 		data->sample_flags |= PERF_SAMPLE_CALLCHAIN;
> > 
> > 		data->size += (1 + data->callchain->nr) * sizeof(u64);
> > 	}
> 
> This is fine as long as all other places (like in PMU drivers) set the
> callchain update the sample data size accordingly.  If not, we can get
> the callchain but the data size will be wrong.

Good point, maybe add a helper there to ensure that code doesn't
duplicate/diverge?