linux-kernel - Re: [PATCH V4 02/16] perf, core: introduce pmu context switch callback

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Date:	Wed, 2 Jul 2014 10:48:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH V4 02/16] perf, core: introduce pmu context switch
 callback

On Mon, Jun 30, 2014 at 04:50:39PM +0800, Yan, Zheng wrote:
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 707617a..71fb77a 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -262,6 +262,12 @@ struct pmu {
>  	 * flush branch stack on context-switches (needed in cpu-wide mode)
>  	 */
>  	void (*flush_branch_stack)	(void);
> +
> +	/*
> +	 * PMU callback for context-switches. optional
> +	 */
> +	void (*sched_task)		(struct perf_event_context *ctx,
> +					 bool sched_in);
>  };

Here you make it a general facility..

> +/*
> + * This function provides the context switch callback to the lower code
> + * layer. It is invoked ONLY when the context switch callback is enabled.
> + */
> +static void perf_pmu_sched_task(struct task_struct *prev,
> +				struct task_struct *next,
> +				bool sched_in)
> +{
> +	struct perf_cpu_context *cpuctx;
> +	struct pmu *pmu;
> +	unsigned long flags;
> +
> +	if (prev == next)
> +		return;
> +
> +	local_irq_save(flags);
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry_rcu(pmu, &pmus, entry) {
> +		if (pmu->sched_task) {
> +			cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
> +
> +			perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +
> +			perf_pmu_disable(pmu);
> +
> +			pmu->sched_task(cpuctx->task_ctx, sched_in);
> +
> +			perf_pmu_enable(pmu);
> +
> +			perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +			/* only CPU PMU has context switch callback */
> +			break;

And here you break it..

> +		}
> +	}
> +
> +	rcu_read_unlock();
> +
> +	local_irq_restore(flags);
> +}

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