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From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>,
	Don Zickus <dzickus@redhat.com>,
	mingo@elte.hu, aris@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] [watchdog] combine nmi_watchdog and softlockup
Date: Fri, 16 Apr 2010 16:59:22 +0200	[thread overview]
Message-ID: <20100416145920.GE5162@nowhere> (raw)
In-Reply-To: <1271429591.4807.2385.camel@twins>

On Fri, Apr 16, 2010 at 04:53:11PM +0200, Peter Zijlstra wrote:
> On Fri, 2010-04-16 at 16:46 +0200, Frederic Weisbecker wrote:
> > > > May be have an arch spin lock there to update your cpu mask safely.
> > > > 
> > > 
> > > Hmm, this is NMI handler path so from what we protect this per-cpu data?
> > > Do I miss something? /me confused
> > 
> > 
> > The cpu mask is not per cpu here, this is a shared bitmap, so you
> > can race against other cpus NMIs.
> > 
> > That said, as I suggested, having a per cpu var that we set when we
> > warned would be much better than a spinlock here. 
> 
> Every time you think NMI and spinlock think FAIL.


In fact I was first inspired by the x86 nmi watchdog handler
that does this spinlock to protect cpumask, but realize just
after my FAIL ;-)


  reply	other threads:[~2010-04-16 14:59 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-04-15 21:25 [PATCH v2] [watchdog] combine nmi_watchdog and softlockup Don Zickus
2010-04-15 22:32 ` Randy Dunlap
2010-04-16 14:12   ` Don Zickus
2010-04-16  1:47 ` Frederic Weisbecker
2010-04-16 14:12   ` Don Zickus
2010-04-16 14:43     ` Frederic Weisbecker
2010-04-16 15:04       ` Don Zickus
2010-04-16 15:32         ` Frederic Weisbecker
2010-04-16 16:14           ` Don Zickus
2010-04-16 16:24             ` Frederic Weisbecker
2010-04-16 14:32   ` Cyrill Gorcunov
2010-04-16 14:46     ` Frederic Weisbecker
2010-04-16 14:53       ` Peter Zijlstra
2010-04-16 14:59         ` Frederic Weisbecker [this message]
2010-04-16 14:54       ` Cyrill Gorcunov
2010-04-16 14:46     ` Don Zickus
2010-04-19 21:21   ` Don Zickus
2010-04-19 21:35     ` Ingo Molnar
2010-04-19 21:51       ` Don Zickus

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