linux-kernel - Re: [PATCH v4 0/9] perf, x86: large PEBS interrupt threshold

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Date:	Thu, 31 Jul 2014 07:50:44 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Yan\, Zheng" <zheng.z.yan@...el.com>,
	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com
Subject: Re: [PATCH v4 0/9] perf, x86: large PEBS interrupt threshold

Peter Zijlstra <peterz@...radead.org> writes:
>
> No feedback on the correctness aspects of the overflow crap?

I assume you mean collisions? See below.

> A quick look at patch 6 reads like you still don't understand the issue
> right. There are no 'collisions' as such in PEBS record generation, or
> are there? See the earlier open discussion.

There can be collisions, but they are in practice extremely rare.

The only way you can get a lot of collision is if you count
the same thing multiple times which is not a useful configuration.
A single monitoring tool only needs a single event once.
While multiple processes may be configuring multiple events
at the same time, they will not start them at the same
time which also prevents collisions.

-Andi

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