linux-kernel - Re: [PATCH v6 2/3]: perf/core: use context tstamp

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Message-ID: <20170822204743.GR32112@worktop.programming.kicks-ass.net>
Date:   Tue, 22 Aug 2017 22:47:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Stephane Eranian <eranian@...gle.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/3]: perf/core: use context tstamp_data for skipped
 events on mux interrupt

On Thu, Aug 10, 2017 at 06:57:43PM +0300, Alexey Budankov wrote:
> The key thing in the patch is explicit updating of tstamp fields for
> INACTIVE events in update_event_times().

> @@ -1405,6 +1426,9 @@ static void update_event_times(struct perf_event *event)
>  	    event->group_leader->state < PERF_EVENT_STATE_INACTIVE)
>  		return;
>  
> +	if (event->state == PERF_EVENT_STATE_INACTIVE)
> +		perf_event_tstamp_update(event);
> +
>  	/*
>  	 * in cgroup mode, time_enabled represents
>  	 * the time the event was enabled AND active

But why!? I thought the whole point was to not need to do this.

The thing I outlined earlier would only need to update timestamps when
events change state and at no other point in time.