linux-kernel - Re: [PATCH] perf, x86: Fall back to vmalloc for BTS buffer allocation

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Message-ID: <20140910185238.GS6758@twins.programming.kicks-ass.net>
Date:	Wed, 10 Sep 2014 20:52:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, eranian@...gle.com, tglx@...utronix.de
Subject: Re: [PATCH] perf, x86: Fall back to vmalloc for BTS buffer allocation

On Wed, Sep 10, 2014 at 11:27:44AM -0700, Andi Kleen wrote:
> > Note that since then we have actually fixed the 'cannot fault from NMI
> > context' thing, so we should be able to actually take those faults. I
> > suspect we can simply remove those WARNs from the vmalloc fault path,
> > but it would need double checking to see if there's no other reasons.
> 
> I think we actually need to use vmalloc_sync_all, because the PEBS/DS
> microcode may do the first access, and those lose events when
> the page is not present.

You'll need to convince Linus: https://lkml.org/lkml/2010/7/14/478
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