Message-ID: <51CB1323.6090305@gmail.com>
Date: Wed, 26 Jun 2013 10:13:23 -0600
From: David Ahern <dsahern@gmail.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Mike Galbraith <bitbucket@online.de>,
        Dave Chiluk <chiluk@canonical.com>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: Scheduler accounting inflated for io bound processes.
References: <51C35C05.1070005@canonical.com> <1372176104.7497.86.camel@marge.simpson.net> <1372182534.7497.129.camel@marge.simpson.net> <20130626093713.GA27385@gmail.com> <20130626104243.GE28407@twins.programming.kicks-ass.net> <20130626155048.GA7399@gmail.com> <51CB110E.6010707@gmail.com> <20130626161051.GA8207@gmail.com>
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On 6/26/13 10:10 AM, Ingo Molnar wrote:
>> Sampled H/W events have an adaptive period that converges to the desired
>> sampling rate. The first few samples come in 10 usecs are so apart and
>> the time period expands to the desired rate. As I recall that adaptive
>> algorithm starts over every time the event is scheduled in.
>
> Yes, but last I checked it (2 years ago? :-) the auto-freq code was
> converging pretty well to the time clock, with little jitter - in essence
> turning it into a fixed-period, fixed-frequency sampling method. That
> would explain Mike's results.

It does converge quickly and stay there for CPU-based events. My point 
was more along the lines that the code is there. Perhaps a tweak to add 
jitter to the period would address fixed period sampling affects.

David
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