linux-kernel - Re: question on sched-rt group allocation cap: sched_rt_runtime

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Message-Id: <93AD5C37-E118-4E5C-8684-EBA548A43492@anirban.org>
Date:	Sun, 6 Sep 2009 17:26:13 -0700
From:	Anirban Sinha <ani@...rban.org>
To:	linux-kernel@...r.kernel.org
Cc:	Fabio Checconi <fchecconi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	a.p.zijlstra@...llo.nl, Dario Faggioli <raistlin@...ux.it>,
	Anirban Sinha <ASinha@...gmasystems.com>
Subject: Re: question on sched-rt group allocation cap: sched_rt_runtime_us



 > Running your program I'm unable to reproduce the same issue on a  
recent
 > kernel here; for 25ms over 100ms across several runs I get less  
than 2%.
 > This number increases, reaching your values, only when using short
 > periods (where the meaning for short depends on your HZ value),


In our kernel, the jiffies are configured as 100 HZ.

 > which
 > is something to be expected, due to the fact that rt throttling uses
 > the tick to charge runtimes to tasks.

Hmm. I see. I understand that.


 > Looking at the git history, there have been several bugfixes to the  
rt
 > bandwidth code from 2.6.26, one of them seems to be strictly  
related to
 > runtime accounting with your setup:

I will apply these patches on Tuesday and rerun the tests.


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