linux-kernel - Re: [PATCH] perf_events: add sampling period randomization support (v2)

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Date:	Thu, 4 Mar 2010 12:32:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	paulus@...ba.org, fweisbec@...il.com, perfmon2-devel@...ts.sf.net,
	robert.richter@....com, eranian@...il.com, davem@...emloft.net,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] perf_events: add sampling period randomization support
 (v2)


* eranian@...gle.com <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.

> +	if (width > 63 || attr->freq)
> +		return -EINVAL;

Why not for freq counters? Those are semi-randomized already, but it might 
make sense to make them 'more' randomized in special circumstances. That would 
also allow us to enable the randomization in perf top and perf record, by 
default.

Without that we'd have no immediate usecase and no way to ensure that this 
code works as intended.

Thanks,

	Ingo
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