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

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Message-ID: <1267518088.25158.0.camel@laptop>
Date:	Tue, 02 Mar 2010 09:21:28 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	fweisbec@...il.com, perfmon2-devel@...ts.sf.net,
	robert.richter@....com, eranian@...il.com
Subject: Re: [PATCH] perf_events: add sampling period randomization support

On Mon, 2010-03-01 at 22:07 -0800, eranian@...gle.com wrote:
> This patch adds support for randomizing the sampling period.
> Randomization is very useful to mitigate the bias that exists
> with sampling. The random number generator does not need to
> be sophisticated. This patch uses the builtin random32()
> generator.
> 
> The user activates randomization by setting the perf_event_attr.random
> field to 1 and by passing a bitmask to control the range of variation
> above the base period. Period will vary from period to period & mask.
> Note that randomization is not available when a target interrupt rate
> (freq) is enabled.
> 
> The last used period can be collected using the PERF_SAMPLE_PERIOD flag
> in sample_type.
> 
> The patch has been tested on X86. There is also code for PowerPC but
> I could not test it.

I don't thikn we need to touch the arch code, we didn't need to for
frequency driven sampling, so I don't see a reason to do so for
randomization either.

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