linux-kernel - Re: [PATCH 4/4] perf, x86: Add PERF_COUNT_HW_NMI

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Message-ID: <BANLkTinVs7_Fm38zosuZ1RcgYRvQicf1Ww@mail.gmail.com>
Date:	Fri, 22 Apr 2011 14:02:01 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Don Zickus <dzickus@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event

Thanks! Looks interesting. Need to think if duch scheme is possible for p4 case.

On Friday, April 22, 2011, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Fri, 2011-04-22 at 13:24 +0400, Cyrill Gorcunov wrote:
>> On Fri, Apr 22, 2011 at 12:54 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>> > On Fri, 2011-04-22 at 12:43 +0400, Cyrill Gorcunov wrote:
>> >> we need a different event and counters for watchdog.
>> >>
>> > Does it count the same thing though? If so we could look at having
>> > alternative encodings support (we might need something like that for
>> > offcore too).
>> >
>>
>> Yes, they count the same thing (well some tech details are different but
>> not much).By using different counters we are allowed to run them
>> simultaneously which makes perf top works again.
>>
>> Could you elaborate what you have in mind with "alternative encodings"
>> here?
>
> Right, so the idea is that one event (concept) has two (or more)
> representations in the config space. And when scheduling the events we
> find we have a conflict, we simply try the alternative encoding(s).
>
> For example, with the offcore bits, we have two events: r1b7 and r1bb
> that both have an extra MSR to fill (01A6 and 01A7 resp). Now if you
> were to write the same value to these MSRs these events would count the
> exact same thing.
>
> So eg. for counting remote dram hits, you can use: r1b7:20ff or
> r1bb:20ff, both count the same. So if we want to support a generic event
> that counts remote dram hits we must pick one. Now if that one is taken
> for measuring some L3 event, we'll have a conflict and not schedule the
> thing, even though the other counter might be available.
>
> POWER has something similar and has already implemented this alternative
> encoding scheme.
>
>
>
>
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