linux-kernel - Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI

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Date:	Tue, 21 Jun 2011 19:26:16 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Vince Weaver <vweaver1@...s.utk.edu>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event v2

On Tue, Jun 21, 2011 at 7:23 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> On Tue, Jun 21, 2011 at 07:10:05PM +0200, Stephane Eranian wrote:
> ...
>> >
>> >  The key here is that we use that named non-sleeping ticks (as oprofile
>> > did) for nmi-watchdog and it allows us to free "cpu-cycles" counter for
>> > user needs. Of course we pick up one counter for this but it doesn't intersect
>> > with "cpu-cycles" counter (because counters are grouped and can count only
>> > specified events in each group). Stepane, should I post more details?
>> >
>> Ok, so you're using a different PMU event for the watchdog. But then, in this
>> case why not simply change kernel/watchdog.c to hardcode something specific
>> for P4, i.e, change the wd_hw_attr.config/type fields to match the
>> event you want.
>
>  It doesn't change things much. Of course I can put some specifics into
> .config but where is the guarantee some new generic event would not ever
> intersect with it. I know (for example) we could reserve -1ULL for this
> event but again where is the guarantee that it will never ever be used
> system wide in future for some different event?
>
I am not talking about a new generic PMU event. I am talking about
you hardcoding a raw event in the callback: type = PERF_TYPE_RAW,
config=0x003c.

> So I need some event-id in which I may be sure it will never be
> used for different purpose.
>
>> You could create a arch specific callback to setup config/type.
>>
>> I don't think it makes sense to expose yet another generic PMU event, especially
>> given the name you gave to it and what it actually does. People might wonder
>> what good is that for?
>
>        Cyrill
>
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