On Thu, Jan 21, 2010 at 11:45 AM, Frederic Weisbecker
<fweis...@gmail.com> wrote:
> On Thu, Jan 21, 2010 at 11:08:12AM +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:
>> - disable all events
>> - rotate the list
>> - collect events from the list
>> - schedule events
>> - activate
>>
>> Collection is the accumulation of events until you have as many as you
>> have counters
>> given you defer scheduling until the end (see loop above).
>>
>> But that does not mean you can schedule what you have accumulated. And then
>> what
>> do you do, i.e., rollback to what?
>
>
>
> If the scheduling validation fails, then you just need to rollback
> the whole group.
>
> That's sensibly what you did in your patch, right? Except the loop
> is now handled by the core code.
>
>
Ok, I think I missed where you were actually placing that loop.
So you want to do this in group_sched_in(), right?
>
> I don't understand why that can't be done with the above model.
> In your patch we iterate through the whole group, collect events,
> and schedule them.
>
> With the above, the collection is just done on enable(), and the scheduling
> is done with the new pmu callbacks.
>
> The thing is sensibly the same, where is the obstacle?
>
There is none. You've just hoisted the some of the code from
hw_perf_group_sched_in().
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