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

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Date:	Tue, 21 Jun 2011 21:54:21 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Stephane Eranian <eranian@...gle.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 07:26:16PM +0200, Stephane Eranian wrote:
...
> >
> >  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.
> 

watchdog.c is system-wide and even if it's not used by archs other
than x86 doesn't mean it'll not in future ;) So we could encode
this watchdog event as you mention (and I would check for this
values and map it internally to bits I need, this btw will require me
to check if this bits do not intersect with some already valid bits
combination but it's a different problem) but than we _must_ be sure it
never bring problems as new arch or consumer appear. So, no, I don't
like this approach, it's fragile. But gimme some time -- I'll re-check
all bits, probably there is some workaround.

	Cyrill
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