linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Date:	Tue, 24 Apr 2007 19:44:45 +0200
From:	Willy Tarreau <w@....eu>
To:	Gene Heskett <gene.heskett@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	David Lang <david.lang@...italinsight.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Davidsen <davidsen@....com>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

On Tue, Apr 24, 2007 at 10:38:32AM -0400, Gene Heskett wrote:
> On Tuesday 24 April 2007, Ingo Molnar wrote:
> >* David Lang <david.lang@...italinsight.com> wrote:
> >> > (Btw., to protect against such mishaps in the future i have changed
> >> > the SysRq-N [SysRq-Nice] implementation in my tree to not only
> >> > change real-time tasks to SCHED_OTHER, but to also renice negative
> >> > nice levels back to 0 - this will show up in -v6. That way you'd
> >> > only have had to hit SysRq-N to get the system out of the wedge.)
> >>
> >> if you are trying to unwedge a system it may be a good idea to renice
> >> all tasks to 0, it could be that a task at +19 is holding a lock that
> >> something else is waiting for.
> >
> >Yeah, that's possible too, but +19 tasks are getting a small but
> >guaranteed share of the CPU so eventually it ought to release it. It's
> >still a possibility, but i think i'll wait for a specific incident to
> >happen first, and then react to that incident :-)
> >
> >	Ingo
> 
> In the instance I created, even the SysRq+b was ignored, and ISTR thats 
> supposed to initiate a reboot is it not?  So it was well and truly wedged.

On many machines I use this on, I have to release Alt while still holding B.
Don't know why, but it works like this.

Willy

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