linux-kernel - Re: [PATCH] perf_events: improve x86 event scheduling (v6 incremental)

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Message-ID: <bd4cb8901001301021r6bc2c720i2be574e9a7ccdb1c@mail.gmail.com>
Date:	Sat, 30 Jan 2010 19:21:55 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	eranian@...il.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net
Subject: Re: [PATCH] perf_events: improve x86 event scheduling (v6 
	incremental)

I will resubmit a patch on Monday. Same thing for AMD NB events.


On Sat, Jan 30, 2010 at 9:56 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, 2010-01-30 at 00:08 +0100, Stephane Eranian wrote:
>> I think there is a problem with this following code:
>>
>> void hw_perf_enable(void)
>>                 for (i = 0; i < cpuc->n_events; i++) {
>>
>>                         event = cpuc->event_list[i];
>>                         hwc = &event->hw;
>>
>>                         if (hwc->idx == -1 || hwc->idx == cpuc->assign[i])
>>                                 continue;
>>
>> Here you are looking for events which are moving. I think the 2nd
>> part of the if is not good enough. It is not because hwc->idx is
>> identical to the assignment, that you can assume the event was
>> already there. It may have been there in the past, then scheduled
>> out and replaced at idx by another event. When it comes back,
>> it gets its spot back, but it needs to be reprogrammed.
>>
>> That is why in v6 incremental, I have added last_cpu, last_tag
>> to have a stronger checks and match_prev_assignment().
>>
>> Somehow it is missing in the series you've committed unless
>> I am missing something.
>
> Right, that went missing because I was assuming that was for the
> optimization of reducing to one loop. And since I didn't see that one
> loop version work I left that part out.
>
> (The risk of doing more than one thing in one patch)
>
> Still, shouldn't be hard to correct, I'll look at doing a patch for this
> on monday, unless you beat me to it :-)
>
>



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