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SubjectRe: [PATCH 08/19] perf c2c: Shared data analyser
On Mon, Mar 03, 2014 at 07:41:17PM +0100, Peter Zijlstra wrote:
> On Mon, Mar 03, 2014 at 01:07:00PM -0500, Joe Mario wrote:
> > If you only sample on the HITMs then you don't get the store misses.
> > That means you'll not be able to detect who is simultaneously tugging
> > on the same cache lines. That gives up much of the value of "perf
> > c2c".
>
> As long as you know which lines are hurting bringing in (loads) you can
> often figure out who is doing the stores on them.

Yes, especially since every store is a load too (unless you're talking
WC)

The method c2c uses is more exact, but keep in mind it's a sampling
heuristic in any cases, with some potential bias. load-latency tags
the loads randomly and there's no guarantee that tagging is fully
uniform. Also you only see a subset in any case.

>
> > As we developed this, we ended up settling on Ivy Bridge to get the
> > behavior we wanted.
>
> Wouldn't SNB also work?

Yes.

Haswell is best however because it can report addresses on far more
events.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.


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