linux-kernel - Re: [PATCH] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4

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Message-ID: <BANLkTinR-pxPKOhGfvuKNCyysZ=k8NDX1g@mail.gmail.com>
Date:	Mon, 27 Jun 2011 21:06:25 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf, x86: Add hw_watchdog_set_attr() in a sake of
 nmi-watchdog on P4

On Mon, Jun 27, 2011 at 9:03 PM, Don Zickus <dzickus@...hat.com> wrote:
> On Thu, Jun 23, 2011 at 04:49:18PM +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 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.
>
> I have tested this on a p4 and a westmere using 'perf top' and then
> lkdtm's 'HARDLOCKUP' command.  Both seemed to work correctly indicating
> that the watchdog and perf were co-existing peacefully. :-)
>

I tested the patch on a P4 and it worked for me too.

Tested-and-reviewed-by: Stephane Eranian <eranian@...gle.com>

I like the patch now. It is far simpler than when we started.
Thanks.

> Thanks Cyrill.
>
> Tested-and-reviewed-by: Don Zickus <dzickus@...hat.com>
>
>> Index: linux-2.6.git/kernel/watchdog.c
>> ===================================================================
>> --- linux-2.6.git.orig/kernel/watchdog.c
>> +++ linux-2.6.git/kernel/watchdog.c
>> @@ -200,6 +200,8 @@ static int is_softlockup(unsigned long t
>>  }
>>
>>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
>> +void __weak hw_nmi_watchdog_set_attr(struct perf_event_attr *wd_attr) { }
>> +
>
> Though I do wonder about this call in the watchdog.  I thought it might be
> better elsewhere but not sure where.
>
> Cheers,
> Don
>
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