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Subject: Re: [PATCH] perf_events: improve x86 event scheduling (v5)
From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
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Date: Thu, 21 Jan 2010 11:11:52 +0100
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On Thu, 2010-01-21 at 11:08 +0100, Stephane Eranian wrote:
> >> > Do you mean this:
> >> >
> >> > hw_perf_group_sched_in_begin(&x86_pmu);
> >> >
> >> > for_each_event(event, group) {
> >> >         event->enable();        //do the collection here
> >> > }
> >> >
> >> >
> >> > if (hw_perf_group_sched_in_end(&x86_pmu)) {
> >> >         rollback...
> >> > }
> >> >
> >> > That requires to know in advance if we have hardware pmu
> >> > in the list though (can be a flag in the group).
> >>
> 
> I don't think this model can work without scheduling for each event.
> 
> Imagine the situation where you have more events than you have
> counters. At each tick you:

No it wont indeed, but it will work for where we now use
hw_perf_group_sched_in() without having to replicate lots of code.

For the cases you mention I see no other way than to try and schedule
each event individually.