Messages in this thread Patch in this message | | | Date | Tue, 15 Nov 2011 14:38:14 +0200 | From | Gleb Natapov <> | Subject | Re: [PATCH RFC] perf, core: disable pmu while context rotation only if needed |
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On Tue, Nov 15, 2011 at 01:07:13PM +0100, Peter Zijlstra wrote: > On Tue, 2011-11-15 at 13:34 +0200, Gleb Natapov wrote: > > > > Currently pmu is disabled and re-enabled on each timer interrupt even > > when no rotation or frequency adjustment is needed. On Intel CPU this > > results in two writes into PERF_GLOBAL_CTRL MSR per tick. On bare metal > > it does not cause significant slowdown, but when running perf in a virtual > > machine it leads to 20% slowdown on my machine. > > > I detest asymmetric locking like that, does something like the below > also work for you? > It does.
> > + if (!rotate && !freq) > + goto done; > + > perf_ctx_lock(cpuctx, cpuctx->task_ctx); > perf_pmu_disable(cpuctx->ctx.pmu); > + > + if (!freq) > + goto rotate; > + Why goto, why not
if (freq) { > perf_ctx_adjust_freq(&cpuctx->ctx, interval); > if (ctx) > perf_ctx_adjust_freq(ctx, interval); }
And the same with next goto.
> > +rotate: > if (!rotate) > - goto done; > + goto unlock; > > cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE); > if (ctx) > @@ -2413,12 +2432,13 @@ static void perf_rotate_context(struct perf_cpu_context *cpuctx) > > perf_event_sched_in(cpuctx, ctx, current); > > +unlock: > + perf_pmu_enable(cpuctx->ctx.pmu); > + perf_ctx_unlock(cpuctx, cpuctx->task_ctx); > + > done: > if (remove) > list_del_init(&cpuctx->rotation_list); > - > - perf_pmu_enable(cpuctx->ctx.pmu); > - perf_ctx_unlock(cpuctx, cpuctx->task_ctx); > } > > void perf_event_task_tick(void)
-- Gleb.
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