linux-kernel - Re: [RFC PATCH 4/4] perf/core: Schedule every pinned events before the the non-pinned

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Date:	Tue, 10 Nov 2009 11:10:13 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 4/4] perf/core: Schedule every pinned events before
 the the non-pinned

On Sun, 2009-11-08 at 21:13 +0100, Frederic Weisbecker wrote:

> +static void
> +__perf_event_sched_in_all(struct perf_event_context *ctx,
> +			  struct perf_cpu_context *cpuctx, int cpu)
> +{
> +	struct perf_event_context *cpu_ctx = &cpuctx->ctx;
> +
> +	/* May require different classes between cpu and task lock */
> +	spin_lock(&cpu_ctx->lock);
> +	spin_lock(&ctx->lock);

Would be good to know for sure, running with lockdep enabled ought to
tell you that pretty quick ;-)

> +	cpu_ctx->is_active = ctx->is_active = 1;
> +
> +	ctx->timestamp = cpu_ctx->timestamp = perf_clock();
> +
> +	perf_disable();
> +
> +	if (cpu_ctx->nr_events)
> +		__perf_event_sched_in_pinned(cpu_ctx, cpuctx, cpu);
> +
> +	if (ctx->nr_events)
> +		__perf_event_sched_in_pinned(cpu_ctx, cpuctx, cpu);
> +
> +	if (cpu_ctx->nr_events)
> +		__perf_event_sched_in_volatile(cpu_ctx, cpuctx, cpu);
> +
> +	if (ctx->nr_events)
> +		__perf_event_sched_in_volatile(cpu_ctx, cpuctx, cpu);
> +
> +	cpuctx->task_ctx = ctx;
> +
> +	perf_enable();
> +
> +	spin_unlock(&ctx->lock);
> +	spin_lock(&cpu_ctx->lock);

I'm pretty sure that ought to be spin_unlock() ;-)

> +}


Like Ingo I don't really like the volatile name.

Can't we simply have 2 lists per cpu a pinned and normal list, and first
schedule all the pinned and RR the normal events?

I guess one could implement that by adding the task context events to
the cpu context events on sched_in and removing them on sched_out. That
would clear up a lot of funny scheduling details.
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