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

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Message-ID: <20130823121004.GW31370@twins.programming.kicks-ass.net>
Date:	Fri, 23 Aug 2013 14:10:04 +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>,
	Johannes Berg <johannes@...solutions.net>
Subject: Re: [sched_delayed] sched: RT throttling activated

On Fri, Aug 23, 2013 at 01:35:24PM +0200, Martin Mokrejs wrote:

> # ps -deo pid,cls,cmd | grep -e 'RR \[' -e 'FF \['

This explicitly only lists kernel threads; from your other comment:

> The shell/python tasks have 'TS' in place of the FF value in the second column
> so I guess they are not requiring realtime responsiveness.

I'll assume you actually inspected the other tasks and found none.

>     7  FF [migration/0]
>    10  FF [watchdog/0]
>    11  FF [watchdog/1]
>    12  FF [migration/1]
>    17  FF [migration/2]
>    22  FF [migration/3]

The 'migration' threads only look like FIFO threads but they're secretly
not and don't count to the limit. The watchdog threads shouldn't run
much either.

>  2161  FF [irq/50-iwlwifi]

Oh a threaded interrupt, I presume you're not using "threadiqrs" since
this is the only interrupt thread around and I see a
'request_threaded_irq()' call in
drivers/net/wireless/iwlwifi/pcie/trans.c

And wow, why would that thing consume that much cpu. 

Johill, ever seen the iwlwifi interrupt go 'funny' and consume gobs of
cpu-time?


> > Nope, you get that message once to tell you that we throttle RT tasks.
> 
> I think the message could improved to explain this is a warn ONCE message and
> that there is no "[sched_delayed] sched: RT throttling deactivated" counterpart
> message to be anticipated.

Would something like: 

  sched: [ONCE] RT throttle hit -- inspect system configuration.

Be a better message?

Also, could you clarify what exact kernel version you're running? I
couldn't find it in your previous messages.
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