Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH 2/7] perf: remove redundant pmu assignment | Date | Mon, 10 Feb 2014 17:44:19 +0000 |
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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 <mark.rutland@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@redhat.com> Cc: Stephane Eranian <eranian@google.com> --- kernel/events/core.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 08659d1..15fe6fc 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2563,8 +2563,6 @@ 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); -- 1.8.1.1
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