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

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Date:	Tue, 21 Jun 2011 18:20:56 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
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

Cyrill,
[repost because of MIME crap]

I admit I don't quite understand how this patch works around
the limitation. In the end you are still going to program some cycle
event into a P4 PMU register. So how it is going to free more counters
for regular users?


On Tue, Jun 21, 2011 at 6:13 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
>
> Ok, I'll take a look (sorry for top posting, ISP problem)
>
> On Tuesday, June 21, 2011, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Tue, 2011-06-21 at 19:40 +0400, Cyrill Gorcunov wrote:
> >> On Tue, Jun 21, 2011 at 7:23 PM, Don Zickus <dzickus@...hat.com> wrote:
> >> > On Thu, Apr 28, 2011 at 07:37:25PM +0400, Cyrill Gorcunov wrote:
> >> >> Due to restriction and specifics of Netburst PMU we need a separated
> >> >> event for NMI watchdog. In particular every Netburst event consume not
> >> >> just a counter and config register, but also an additional ESCR register.
> >> >> Since ESCR registers are grouped upon counters (i.e. if ESCR is occupied
> >> >> for some event there is no room for another event to enter the room until
> >> >> it's released) we need to pick up "least" used ESCR (or most available)
> >> >> for nmi-watchdog purpose -- MSR_P4_CRU_ESCR2/3 was chosen.
> >> >>
> >> >> Note that on all other PMUs which support relocation of events between
> >> >> counters this event is a simple alias for PERF_COUNT_HW_CPU_CYCLES.
> >> >
> >> > Cyril,
> >> >
> >> > What ever happened with this patch?
> >> >
> >> > Cheers,
> >> > Don
> >> >
> >>
> >> Well, it's flowing around, I didn't get any more Ack's other than your. Since it
> >> introduces kind of abi I presume more ack's would be welcome before it
> >> (possibly) get merged.
> >
> > we could avoid that abi thing by simply not making it an exposed event
> >
> > Its not like userspace ever should be using it anyway
> >
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