linux-kernel - Re: [PATCH v2] perf: fix perf_event

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Date:   Tue, 14 Mar 2023 20:58:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <song@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v2] perf: fix perf_event_context->time

On Mon, Mar 13, 2023 at 10:16:08AM -0700, Song Liu wrote:
> Time readers rely on perf_event_context->[time|timestamp|timeoffset] to get
> accurate time_enabled and time_running for an event. The difference between
> ctx->timestamp and ctx->time is the among of time when the context is not
> enabled. __update_context_time(ctx, false) is used to increase timestamp,
> but not time. Therefore, it should only be called in ctx_sched_in() when
> EVENT_TIME was not enabled.
> 
> Fixes: 09f5e7dc7ad7 ("perf: Fix perf_event_read_local() time")
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Acked-by: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Song Liu <song@...nel.org>

Looks like I'm wearing another brown paper bag tonight..

Thanks!