Messages in this thread | | | Date | Mon, 8 Aug 2016 14:12:46 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf: sched out groups atomically |
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On Tue, Jul 26, 2016 at 06:12:21PM +0100, Mark Rutland wrote: > Groups of events are supposed to be scheduled atomically, such that it > is possible to derive meaningful ratios between their values. > > We take great pains to achieve this when scheduling event groups to a > PMU in group_sched_in(), calling {start,commit}_txn() (which fall back > to perf_pmu_{disable,enable}() if necessary) to provide this guarantee. > However we don't mirror this in group_sched_out(), and in some cases > events will not be scheduled out atomically. > > For example, if we disable an event group with PERF_EVENT_IOC_DISABLE, > we'll cross-call __perf_event_disable() for the group leader, and will > call group_sched_out() without having first disabled the relevant PMU. > We will disable/enable the PMU around each pmu->del() call, but between > each call the PMU will be enabled and events may count. > > Avoid this by explicitly disabling and enabling the PMU around event > removal in group_sched_out(), mirroring what we do in group_sched_in().
Thanks!
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