Messages in this thread | | | From | Song Liu <> | Subject | Re: [RFC][PATCH] perf: Rewrite core context handling | Date | Tue, 16 Oct 2018 16:34:05 +0000 |
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> On Oct 16, 2018, at 2:50 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Sat, Oct 13, 2018 at 08:31:37AM +0000, Song Liu wrote: > >> The only suggestion I have right now is on which struct owns which >> data: >> >> 1. perf_cpu_context owns two perf_event_context: ctx and *task_ctx. >> This is the same as right now. > >> 2. perf_event_context owns multiple perf_event_pmu_context: >> One perf_event_pmu_context for software groups; >> One perf_event_pmu_context for each hardware PMU. > > It does now already, right? Through the pmu_ctx_list we can, given an > perf_event_context, find all associated perf_event_pmu_context's.
Yes, this is very similar to right now. It is related to #4, #5 below. With current patch, perf_cpu_pmu_context is more like the "owner" of the per CPU perf_event_pmu_context. I feel it is more natural that perf_cpu_context is the owner of perf_event_pmu_context, while the perf_cpu_pmu_context doesn't own anything.
Again, the difference to current patch is very small.
> >> 3. perf_event_pmu_context owns RB tree of events. Since we don't >> need rotation across multiple hardware PMUs, the rotation is >> within same perf_event_pmu_context. > > By keeping the RB trees in perf_event_context, we get bigger trees, > which is more efficient (log(n+m) < log(n) + log(m)) > > Also, specifically, it means we only need a single merge sort / > iteration to schedule in a full context, instead of (again) doing 'n' of > them. > > Also, given a context and a pmu, it is cheaper for finding the relevant > events; this is needed for big.little for instance. Something the > proposed patch doesn't fully flesh out.
Would it be faster if we add a perf_event_pmu_context pointer to the perf_event? I think a group on hw PMU-a should never know a group on hw PMU-b. So some separation would make things simpler.
Thanks, Song
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