linux-kernel - Re: [PATCH] perf, x86: Optimize intel_pmu_pebs_fixup

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Date:	Fri, 18 Oct 2013 00:01:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Don Zickus <dzickus@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
	dave.hansen@...ux.intel.com, Stephane Eranian <eranian@...gle.com>,
	jmario@...hat.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] perf, x86: Optimize intel_pmu_pebs_fixup_ip()

On Thu, Oct 17, 2013 at 11:26:23AM -0700, Linus Torvalds wrote:
> On Thu, Oct 17, 2013 at 9:30 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > So avoid having to call copy_from_user_nmi() for every instruction.
> > Since we already limit the max basic block size, we can easily
> > pre-allocate a piece of memory to copy the entire thing into in one
> > go.
> 
> copy_from_user_nmi() itself is all kinds of nasty.

Oh wait,.. now that Steven fixed being able to take faults from NMI
context; we could actually try copy_from_user_inatomic(). Being able to
directly access userspace would make the whole deal a lot easier again.

I'll go try this tomorrow.
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