Messages in this thread | | | Date | Mon, 10 Feb 2014 19:10:26 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 7/7] perf: kill perf_event_context::pmu |
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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.
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