Re: [PATCH v2 4/7] perf, x86: Save/resotre LBR stack during contextswitch
From: Peter Zijlstra
Date: Thu Jul 04 2013 - 08:46:59 EST
On Mon, Jul 01, 2013 at 03:23:04PM +0800, Yan, Zheng wrote:
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@@ -2488,25 +2508,31 @@ static void perf_branch_stack_sched_in(struct task_struct *prev,
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>
list_for_each_entry_rcu(pmu, &pmus, entry) {
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cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
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+ task_ctx = cpuctx->task_ctx;
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>
/*
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- * check if the context has at least one
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- * event using PERF_SAMPLE_BRANCH_STACK
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+ * force flush the branch stack if there are cpu-wide events
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+ * using PERF_SAMPLE_BRANCH_STACK
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+ *
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+ * save/restore the branch stack if the task context has
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+ * at least one event using PERF_SAMPLE_BRANCH_STACK
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*/
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- if (cpuctx->ctx.nr_branch_stack > 0
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- && pmu->flush_branch_stack) {
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-
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+ bool force_flush = cpuctx->ctx.nr_branch_stack > 0;
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+ if (pmu->branch_stack_sched &&
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+ (force_flush ||
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+ (task_ctx && task_ctx->nr_branch_stack > 0))) {
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pmu = cpuctx->ctx.pmu;
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- perf_ctx_lock(cpuctx, cpuctx->task_ctx);
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+ perf_ctx_lock(cpuctx, task_ctx);
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perf_pmu_disable(pmu);
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- pmu->flush_branch_stack();
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+ pmu->branch_stack_sched(task_ctx,
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+ sched_in, force_flush);
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perf_pmu_enable(pmu);
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- perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
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+ perf_ctx_unlock(cpuctx, task_ctx);
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}
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}
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I never really like this; and yes I know I wrote part of that. Is there
any way we can get rid of this and to it 'properly' through the events
that get scheduled?
After all; the LBR usage is through the events, so scheduling the events
should also manage the LBR state.
What is missing for that to work?
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