linux-kernel - Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set

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Message-ID: <20110705152515.GE4060@sun>
Date:	Tue, 5 Jul 2011 19:25:16 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Don Zickus <dzickus@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a
 sake of nmi-watchdog on P4

On Tue, Jul 05, 2011 at 04:56:56PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Tue, 2011-07-05 at 15:31 +0200, Ingo Molnar wrote:
> > > So there's lots of options to fix/improve this more intelligently.
> > 
> > Sure, and I like the alternative encoding thing best, but doing 
> > that will take time, in the meantime this patch, which is 
> > relatively small (and easy to revert once we get something better 
> > going) does fix a problem for those few unfortunate souls still 
> > using P4 hardware.
> 
> Well, the BUS_CYCLES thing looks similarly straightforward and should 
> result in an even simpler patch.
>

nope, bus cycles count fsb driving which is not the same as execution unit
productions, so I fear it is not that reliable and i guess (note _guess_ here
since I can't prove it without hardware handy :) if cpus are stuck with endless
loop inside kernel we might miss such lockup (hard scenario, since there
will be activity on fsb anyway, but still).

> On P4 BUS_CYCLES would be able to co-exist with CPU_CYCLES so it will 
> solve the P4 issue naturally as well.
> 
> Thanks,
> 
> 	Ingo

i don't think it changes much, Ingo, if I change it to bus cycles I still
will have to setup nmi-watchdog event separately (but simply with bus
event).

so an only option is the aliases, i'll try to deal with it but no milestones

	Cyrill
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