linux-kernel - Re: [rfc patch v2] rt,nohz_full: fix nohz_full for PREEMPT_RT

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Message-ID: <1426567522.12107.8.camel@gmail.com>
Date:	Tue, 17 Mar 2015 05:45:22 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	John Kacur <jkacur@...hat.com>
Subject: Re: [rfc patch v2] rt,nohz_full: fix nohz_full for PREEMPT_RT_FULL

On Tue, 2015-03-17 at 02:53 +0100, Mike Galbraith wrote:
> On Mon, 2015-03-16 at 21:24 +0100, Sebastian Andrzej Siewior wrote:

> > What you do is that you accept the fact that the timer-softirq is
> > scheduled for no reason and then you try to disable the tick from within
> > the timer-softirq. I assumed that it would work get the "expired timer"
> > somehow.
> 
> Yup, it works around that otherwise crippling wakeup.  If I re-apply..
> 
>      timers-do-not-raise-softirq-unconditionally.patch
> 
> ..the workaround is not needed of course, but the livelock fix still is.
> I haven't yet tested that in 3.18-rt though, only 4.0-rt, but I presume
> it'll be the same deal there when I do.

Did that, and it is.  Fire up tbench 4 + make -j4 on my i7-4790+smt box
booted nohz_full=2,3,6,7, death spiral begins shortly thereafter.

	-Mike

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