Messages in this thread | | | Date | Mon, 9 Nov 2020 18:40:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/3] perf/core: Flush PMU internal buffers for per-CPU events |
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On Mon, Nov 09, 2020 at 09:49:31AM -0500, Liang, Kan wrote:
> - The patch 1 tries to fix broken per-CPU events. The CPU context cannot be > retrieved from the task->perf_event_ctxp. So it has to be tracked in the > sched_cb_list. Yes, the code is very similar to the original codes, but it > is actually the new code for per-CPU events. The optimization for per-task > events is still kept. > For the case, which has both a CPU context and a task context, yes, the > __perf_pmu_sched_task() in this patch is not invoked. Because the > sched_task() only need to be invoked once in a context switch. The > sched_task() will be eventually invoked in the task context. > > > - The following patch 3 tries to optimize the sched_task() further. > - We handle the per-CPU event and per-task event in different places. In a > pure per-task context, we don't need to go through the sched_cb_list. We can > get the information from task->perf_event_ctxp. We introduce a flag to > distinguish them. > - For most of the cases, we don't need to invoke the sched_task() in both > sched in and sched out. We also introduce a flag for PMUs to avoid > unnecessary calls. >
There's a further optimiation possible; we can have pmu::swap_task_ctx() imply pmu::sched_task() (both in and out).
It's all a bit of a mess though.. let me consider.
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