Messages in this thread | | | Date | Wed, 12 Feb 2014 15:01:49 +0000 | From | Dave Martin <> | Subject | Re: [PATCH 7/7] perf: kill perf_event_context::pmu |
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On Tue, Feb 11, 2014 at 05:56:51PM +0000, Mark Rutland wrote: > On Mon, Feb 10, 2014 at 06:10:26PM +0000, Peter Zijlstra wrote: > > On Mon, Feb 10, 2014 at 05:44:24PM +0000, Mark Rutland wrote: > > > Currently portions of the perf subsystem assume that a > > > perf_event_context is associated with a single pmu while in reality a > > > single perf_event_context may be shared by a number of pmus, as commit > > > 443772776c69 (perf: Disable all pmus on unthrottling and rescheduling) > > > describes. > > > > > > This patch removes perf_event_context::pmu, replacing it with a direct > > > pointer to the associated perf_cpu_context and a task_ctx_nr (as all > > > pmus sharing a context have the same task_ctx_nr). This makes the > > > relationship between pmus and perf_event_contexts clearer and allows us > > > to save on some pointer chasing. > > > > > > This also fixes a potential misuse of ctx->pmu introduced in commit > > > bad7192b842c (perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the > > > period), where ctx->pmu is disabled before modifying state on > > > event->pmu. In this case the two pmus are not guaranteed to be the same. > > > > > > As perf_pmu_rotate_{start,stop} only really care about the context they > > > are rotating, they are renamed to perf_event_ctx_{start,stop}. > > > > This very much relies on the previous patch where you make pmu_disable > > iterate all the events. > > > > We could also change this to keep a pmu list for each context and > > iterate that instead. Given there is indeed a fair limit on different > > PMUs in the system that iteration should be much shorter. > > Another option would be to have a context per-pmu. Each context's pmu > pointer would be valid, and (other than the case of software events) it > doesn't make sense to place events from disparate PMUs into the same > group anyway. Then you don't need a fixed sized pmu list in the context > or some arcane list structs.
Getting event rotation to work in a sensible way when there are mixtures of events for different PMUs in a single context. I've not come up with a good enough solution for that to post yet.
Splitting out each PMU as a separate hardware context would make this work a lot more naturally.
Cheers ---Dave
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