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

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Date:	Thu, 4 Mar 2010 09:52:56 +0100
From:	Robert Richter <robert.richter@....com>
To:	eranian@...gle.com
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	paulus@...ba.org, fweisbec@...il.com, perfmon2-devel@...ts.sf.net,
	eranian@...il.com, davem@...emloft.net
Subject: Re: [PATCH] perf_events: add sampling period randomization support
 (v2)

On 02.03.10 16:21:45, 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.
> 
> Randomization is activated by setting perf_event_attr.random_period_width
> to a non-zero value. It represents the width of the mask to apply to the
> random value, i.e, maximum range of variation. The random value is applied
> AROUND the period, i.e., period may be longer or shorter with a maximum
> variation of half the bit width. Thus, on average the sampling period remains
> equal to the initial period passed in perf_event_attr.sample_period.
> 
> 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.
> 
> Randomization is implemented in generic code thus it applies to all
> PMU models and software events.
> 
> 	Signed-off-by: Stephane Eranian <eranian@...gle.com>
> 
> --
>  include/linux/perf_event.h |    3 +++
>  kernel/perf_event.c        |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)

Reviewed-by: Robert Richter <robert.richter@....com>

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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