Re: question on sched-rt group allocation cap: sched_rt_runtime_us

From: Anirban Sinha
Date: Sun Sep 06 2009 - 20:26:38 EST

> 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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