linux-kernel - Re: [sched_delayed] sched: RT throttling activated

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Message-ID: <20130823100913.GQ31370@twins.programming.kicks-ass.net>
Date:	Fri, 23 Aug 2013 12:09:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Martin Mokrejs <mmokrejs@...d.natur.cuni.cz>
Cc:	Theodore Tso <tytso@....edu>, Thomas Gleixner <tglx@...utronix.de>,
	mingo@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [sched_delayed] sched: RT throttling activated

On Fri, Aug 23, 2013 at 10:53:02AM +0200, Martin Mokrejs wrote:
> Hi,
>   I tried to figure out what this message really means. I came to 
> https://rt.wiki.kernel.org/index.php/Frequently_Asked_Questions
> but I am still lost. I lack in the FAQ some user-related information.
> The first paragraph is still unclear to me. I have a i7-2640M based
> laptop, hyperthreading is enabled by BIOS but I shut down the two
> emulated cores by (no BIOS option to disable HT):
> 
> Would you please clarify what the "[sched_delayed] sched: RT throttling activated"
> really means? 

It means you have (a) real-time task(s) that consume significant amount
of time. At some point we throttle them in an attempt to keep the system
from falling over.

> Is that because there is some RT-requiring application on my system?

Yep.

> I don't know of any (or don't care about real-time responsiveness except that ALSA
> drivers require me to have CONFIG_SND_HRTIMER=y). Per Goggle answers could the
> culprit be nfsd? Then I will recompile is as a module.

Unlikely, I don't think I've ever seen anybody run their nfsd with RT
priority. Also, you can run RT tasks regardless of the config options.
SCHED_RR and SCHED_FIFO are POSIX specified and always available.
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