linux-kernel - Re: [RFC][PATCH 13/19] perf: Per cpu-context rotation timer

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Date:	Tue, 07 Sep 2010 19:08:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulus <paulus@...ba.org>
Cc:	stephane eranian <eranian@...glemail.com>,
	Robert Richter <robert.richter@....com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Yanmin <yanmin_zhang@...ux.intel.com>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 13/19] perf: Per cpu-context rotation timer

On Tue, 2010-09-07 at 18:46 +0200, Peter Zijlstra wrote:
> +static enum hrtimer_restart perf_event_context_tick(struct hrtimer
> *timer)
>  {
> +       enum hrtimer_restart restart = HRTIMER_NORESTART;
>         struct perf_cpu_context *cpuctx;
>         struct perf_event_context *ctx;
>         int rotate = 0;
>  
> +       cpuctx = container_of(timer, struct perf_cpu_context, timer);
>  
> +       if (cpuctx->ctx.nr_events) {
> +               restart = HRTIMER_RESTART;
> +               if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
> +                       rotate = 1;
> +       }
>  
> +       ctx = current->perf_event_ctxp;
> +       if (ctx && ctx->nr_events) {
> +               restart = HRTIMER_RESTART;
> +               if (ctx->nr_events != ctx->nr_active)
> +                       rotate = 1;
> +       } 

Note to self, this is probably racy against pmu_rotate_start().
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