lkml.org 
[lkml]   [2015]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH v0 3/5] perf: Introduce instruction trace filtering
Date
Peter Zijlstra <peterz@infradead.org> writes:

> On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
>> +static int __perf_event_itrace_filters_setup(void *info)
>> +{
>> + struct perf_event *event = info;
>> + int ret;
>> +
>> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE)
>> + return -EAGAIN;
>> +
>> + /* matches smp_wmb() in event_sched_in() */
>> + smp_rmb();
>> +
>> + /*
>> + * There is a window with interrupts enabled before we get here,
>> + * so we need to check again lest we try to stop another cpu's event.
>> + */
>> + if (READ_ONCE(event->oncpu) != smp_processor_id())
>> + return -EAGAIN;
>> +
>> + event->pmu->stop(event, PERF_EF_UPDATE);
>> + rcu_read_lock();
>> + ret = event->pmu->itrace_filter_setup(event);
>> + rcu_read_unlock();
>> + event->pmu->start(event, PERF_EF_RELOAD);
>
> Would it not be more sensible to let the ::itrace_filter_setup() method
> do the stop/start-ing if and when needed?

I don't have a strong opinion on this, the only question is, are we
comfortable with pmu driver callback doing the
rcu_read_lock/unlock, because it still needs to iterate the filter list.
Other than that it's probably a good idea.

Thanks,
--
Alex


\
 
 \ /
  Last update: 2015-12-11 16:41    [W:0.161 / U:0.924 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site