From fdded676c3ef680bf1abc415d307d7e69a6768d1 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 10 Feb 2014 17:44:19 +0000 Subject: [PATCH] perf: Remove redundant PMU assignment Currently perf_branch_stack_sched_in iterates over the set of pmus, checks that each pmu has a flush_branch_stack callback, then overwrites the pmu before calling the callback. This is either redundant or broken. In systems with a single hw pmu, pmu == cpuctx->ctx.pmu, and thus the assignment is redundant. In systems with multiple hw pmus (i.e. multiple pmus with task_ctx_nr == perf_hw_context) the pmus share the same perf_cpu_context. Thus the assignment can cause one of the pmus to flush its branch stack repeatedly rather than causing each of the pmus to flush their branch stacks. Worse still, if only some pmus have the callback the assignment can result in a branch to NULL. This patch removes the redundant assignment. Signed-off-by: Mark Rutland Acked-by: Will Deacon Signed-off-by: Peter Zijlstra Cc: Stephane Eranian Link: http://lkml.kernel.org/r/1392054264-23570-3-git-send-email-mark.rutland@arm.com Signed-off-by: Ingo Molnar --- kernel/events/core.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 425159882a6f..823a53d72d6a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2582,8 +2582,6 @@ static void perf_branch_stack_sched_in(struct task_struct *prev, 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);