linux-kernel - Re: [PATCH] perf_events: add sampling period randomization support

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Message-ID: <1267530078.25158.41.camel@laptop>
Date:	Tue, 02 Mar 2010 12:41:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <robert.richter@....com>
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	paulus@...ba.org, fweisbec@...il.com, perfmon2-devel@...ts.sf.net,
	eranian@...il.com
Subject: Re: [PATCH] perf_events: add sampling period randomization support

On Tue, 2010-03-02 at 11:53 +0100, Robert Richter wrote:
> 
> Only adding the random value will lead to longer sample periods on
> average. To compensate this you could calculate something like:
> 
>          event->hw.sample_period = event->attr.sample_period + (new_seed & mask) - (mask >> 1);

Or cheat and do something like:

  sample_period ^= (new_seed & mask);

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