linux-kernel - Re: [stable] scheduler nice 19 versus 'idle' behavior / static low-priority scheduling

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Date:	Mon, 2 Feb 2009 15:57:14 -0800
From:	Greg KH <greg@...ah.com>
To:	Mike Galbraith <efault@....de>
Cc:	Brian Rogers <brian@...w.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Ingo Molnar <mingo@...e.hu>,
	Nathanael Hoyle <nhoyle@...letech.com>,
	stable <stable@...nel.org>
Subject: Re: [stable] scheduler nice 19 versus 'idle' behavior / static
	low-priority scheduling

On Sat, Jan 31, 2009 at 10:08:13AM +0100, Mike Galbraith wrote:
> On Sat, 2009-01-31 at 06:38 +0100, Mike Galbraith wrote:
> > On Fri, 2009-01-30 at 14:12 -0800, Brian Rogers wrote:
> > > Mike Galbraith wrote:
> > > > On Fri, 2009-01-30 at 02:59 -0500, Nathanael Hoyle wrote:
> > > >   
> > > >> I am running foldingathome under it at the moment, and it seems to be
> > > >> improving the situation somewhat, but I still need/want to test with
> > > >> Mike's referenced patches.
> > > >>     
> > > > You will most definitely encounter evilness running SCHED_IDLE tasks in
> > > > a kernel without the SCHED_IDLE fixes.
> > > >   
> > > Speaking of SCHED_IDLE fixes, is 
> > > 6bc912b71b6f33b041cfde93ca3f019cbaa852bc going to be put into the next 
> > > stable 2.6.28 release? Without it on 2.6.28.2, I can still produce 
> > > minutes-long freezes with BOINC or other idle processes.
> > > 
> > > With the above commit on top of 2.6.28.2 and also 
> > > cce7ade803699463ecc62a065ca522004f7ccb3d, the problem is solved, though 
> > > I assume cce7ad isn't actually required to fix that, and I can test that 
> > > if desired.
> > 
> > I think they both should go to stable, but dunno if they're headed that
> > direction or not.
> > 
> > One way to find out, CCs added.
> 
> For those who may want to run SCHED_IDLE tasks in .27, I've integrated
> and lightly tested the fixes required to do so.  One additional commit
> was needed to get SCHED_IDLE vs nice 19 working right, namely f9c0b09.
> Without that, SCHED_IDLE tasks received more CPU than nice 19 tasks.
> 
> Since .27 is in long-term maintenance, I'd integrate into stable, but
> that's not my decision.  Anyone who applies the below to their stable
> kernel gets to keep all the pieces should something break ;-)

I'm going to hold off and not do this, as it seems too risky.

But thanks for the pointers, perhaps someone else will want to do this
for their distro kernels if they have problems with this.

thanks,

greg k-h
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