linux-kernel - Re: [PATCH 09/12] perf_events: add hook to flush branch

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Date:	Mon, 05 Dec 2011 22:37:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, acme@...hat.com,
	ming.m.lin@...el.com, andi@...stfloor.org, robert.richter@....com,
	ravitillo@....gov, will.deacon@....com, paulus@...ba.org,
	benh@...nel.crashing.org, rth@...ddle.net, ralf@...ux-mips.org,
	davem@...emloft.net, lethal@...ux-sh.org
Subject: Re: [PATCH 09/12] perf_events: add hook to flush branch_stack on
 context switch (v2)

On Fri, 2011-10-14 at 14:37 +0200, Stephane Eranian wrote:
> +               /*
> +                * check if the context has at least one
> +                * event using PERF_SAMPLE_BRANCH_STACK
> +                */
> +               if (cpuctx->ctx.nr_branch_stack > 0
> +                   && pmu->flush_branch_stack) {
> +
> +                       pmu = cpuctx->ctx.pmu;
> +
> +                       perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +
> +                       perf_pmu_disable(pmu);
> +
> +                       pmu->flush_branch_stack();
> +
> +                       perf_pmu_enable(pmu);
> +
> +                       perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +               }
> +       } 

(what whitespace looks funny)

So all PMUs not supporting this branch stuff will fail to create a
has_branch_stack() event, right? Thus all ctx with !0 nr_branch_stack
support it. Doesn't this make the test for pmu->flush_branch_stack
redundant?


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