Messages in this thread Patch in this message | | | Date | Fri, 25 Nov 2016 08:26:01 +0900 | From | Namhyung Kim <> | Subject | Re: [PATCH 02/14] perf/x86: output NMI overhead |
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On Thu, Nov 24, 2016 at 07:40:21PM +0000, Liang, Kan wrote: > > > > > @@ -1492,8 +1507,10 @@ perf_event_nmi_handler(unsigned int cmd, > > struct pt_regs *regs) > > > start_clock = sched_clock(); > > > ret = x86_pmu.handle_irq(regs); > > > finish_clock = sched_clock(); > > > + clock = finish_clock - start_clock; > > > > > > - perf_sample_event_took(finish_clock - start_clock); > > > + perf_caculate_nmi_overhead(clock); > > > + perf_sample_event_took(clock); > > > > Ah, so it's the *sampling* overhead, not the NMI overhead. > > > > This doesn't take into account the cost of entering/exiting the handler, > > which could be larger than the sampling overhead (e.g. if the PMU is > > connected through chained interrupt controllers). > > > > > enum perf_record_overhead_type { > > > + PERF_NMI_OVERHEAD = 0, > > > > As above, it may be worth calling this PERF_SAMPLE_OVERHEAD; this > > I think PERF_NMI stands for the NMI overhead in perf part. > > PERF_SAMPLE_OVERHEAD looks too generic I think. > It heard like the sum of all overheads in sampling. > After all we collect the overhead in different stage of sampling. > NMI handler, multiplexing, side-band events... > > > > doesn't count the entire cost of the NMI, and other architectures may want > > to implement this, yet don't have NMI. > > > > I think I can change it to PERF_X86_NMI_OVERHEAD, if you think it's more clear. > For other architectures, they can implement their own type of overhead, > just ignore the NMI one.
I think it'd be better making it arch-agnostic if possible. What about PERF_PMU_OVERHEAD or PERF_PMU_SAMPLE_OVERHEAD?
Thanks, Namhyung
> > > > > > @@ -1872,7 +1873,7 @@ __perf_remove_from_context(struct perf_event > > > *event, { > > > unsigned long flags = (unsigned long)info; > > > > > > - event_sched_out(event, cpuctx, ctx); > > > + event_sched_out(event, cpuctx, ctx, false); > > > if (flags & DETACH_GROUP) > > > perf_group_detach(event); > > > list_del_event(event, ctx); > > > @@ -1918,9 +1919,9 @@ static void __perf_event_disable(struct > > perf_event *event, > > > update_cgrp_time_from_event(event); > > > update_group_times(event); > > > if (event == event->group_leader) > > > - group_sched_out(event, cpuctx, ctx); > > > + group_sched_out(event, cpuctx, ctx, true); > > > else > > > - event_sched_out(event, cpuctx, ctx); > > > + event_sched_out(event, cpuctx, ctx, true); > > > > Why does this differ from __perf_remove_from_context()? > > > > Both of them are called on removing event. So I think we only > need to log overhead in one place. > > I just did some tests. It looks __perf_remove_from_context is called > after __perf_event_disable. > I think I will log overhead in __perf_remove_from_context for next > version. > > > > What's the policy for when we do or do not measure overhead? > > Currently, it's enabled all the time. > Jirka suggested me to make it configurable. I will do it in next version. > For next version, I still prefer to make it enable by default, since > it doesn't bring additional overhead based on my test. > > Thanks, > Kan
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