Messages in this thread | | | Date | Wed, 12 Sep 2012 16:43:38 +0200 | Subject | Re: [PATCH v2 2/3] perf: use hrtimer for event multiplexing | From | Stephane Eranian <> |
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On Wed, Sep 12, 2012 at 4:22 PM, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, 2012-09-12 at 16:13 +0200, Stephane Eranian wrote: >> +static DEFINE_PER_CPU(struct list_head, rotation_list); > > Why do you keep the rotation list? The only use seems to be: > > >> +void perf_cpu_hrtimer_cancel(int cpu) >> +{ >> + struct list_head *head = &__get_cpu_var(rotation_list); >> + struct perf_cpu_context *cpuctx, *tmp; >> + unsigned long flags; >> + >> + if (WARN_ON(cpu != smp_processor_id())) >> + return; >> + >> + local_irq_save(flags); >> + >> + list_for_each_entry_safe(cpuctx, tmp, head, rotation_list) { >> + if (cpuctx->hrtimer_active) { >> + hrtimer_cancel(&cpuctx->hrtimer); >> + cpuctx->hrtimer_active = 0; >> + } >> + } >> + >> + local_irq_restore(flags); >> +} > > Which is weird, why not use the existing for-each-pmu loop in > perf_event_exit_cpu_context() ? Or something similar to iterate all > extant PMUs and thus their cpuctxs? > True. That would probably work too.
> Also, you can do away with hrtimer_active, you can hrtimer_cancel() on > an inactive hrtimer just fine, it will DTRT.
The hrtimer_active is used to prevent activating the timer multiple times in a row.
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