linux-kernel - Re: [PATCH 9/9] x86/UV: Add ability to disable UV NMI handler

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Message-ID: <20130909124349.GY31370@twins.programming.kicks-ass.net>
Date:	Mon, 9 Sep 2013 14:43:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Travis <travis@....com>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jason Wessel <jason.wessel@...driver.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dimitri Sivanich <sivanich@....com>,
	Hedi Berriche <hedi@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] x86/UV: Add ability to disable UV NMI handler

On Thu, Sep 05, 2013 at 05:50:41PM -0500, Mike Travis wrote:
> For performance reasons, the NMI handler may be disabled to lessen the
> performance impact caused by the multiple perf tools running concurently.
> If the system nmi command is issued when the UV NMI handler is disabled,
> the "Dazed and Confused" messages occur for all cpus.  The NMI handler is
> disabled by setting the nmi disabled variable to '1'.  Setting it back to
> '0' will re-enable the NMI handler.

I'm not entirely sure why this is still needed now that you've moved all
really expensive bits into the UNKNOWN handler.
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