linux-kernel - Re: perf_event: rdpmc self-monitoring overhead issue

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Date:	Mon, 2 Sep 2013 09:15:48 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	eranian@...il.com
cc:	Andi Kleen <andi@...stfloor.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: perf_event: rdpmc self-monitoring overhead issue

On Mon, 2 Sep 2013, Stephane Eranian wrote:

> On Mon, Sep 2, 2013 at 4:50 AM, Andi Kleen <andi@...stfloor.org> wrote:
> > Stephane Eranian <eranian@...glemail.com> writes:
> >
> >> I don't see a flag in mmap() to fault it in immediately.
> >
> > MAP_PRESENT
> >
> I could not find this constant defined anywhere in the kernel source tree
> nor in /usr/include. Are you sure of the name?

I assume he means MAP_POPULATE

which does improve things, from ~3000 cycles to ~219 cycles but that's 
still more overhead than the ~130 or so you get by manually touching the 
page first.

Vince

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