Re: perf_event: rdpmc self-monitoring overhead issue

[Vince Weaver]

On Mon, 2 Sep 2013, Stephane Eranian wrote:

> On Mon, Sep 2, 2013 at 4:50 AM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> > Stephane Eranian <eranian@xxxxxxxxxxxxxx> 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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