Date: Mon, 24 Nov 2008 09:11:13 -0600
From: Dimitri Sivanich <sivanich@sgi.com>
To: Li Zefan <lizf@cn.fujitsu.com>, Gregory Haskins <ghaskins@novell.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>, Derek Fults <dfults@sgi.com>,
       Peter Zijlstra <peterz@infradead.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: RT sched: cpupri_vec lock contention with def_root_domain and no load balance
Message-ID: <20081124151113.GB2292@sgi.com>
References: <20081104144017.GB30855@sgi.com> <4910634C.1020207@novell.com> <49246DD0.3010509@qualcomm.com> <4924762B.8000108@novell.com> <4924C770.7050107@qualcomm.com> <4926158B.9020909@novell.com> <49271449.2030804@qualcomm.com> <20081121211800.GA16647@sgi.com> <4927AECA.2040707@qualcomm.com> <4927C055.8030009@cn.fujitsu.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4927C055.8030009@cn.fujitsu.com>
User-Agent: Mutt/1.5.13 (2006-08-11)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1666
Lines: 32

On Sat, Nov 22, 2008 at 04:18:29PM +0800, Li Zefan wrote:
> Max Krasnyansky wrote:
> > 
> > Dimitri Sivanich wrote:
> >>
> >> Which is the way sched_load_balance is supposed to work. You need to set
> >> sched_load_balance=0 for all cpusets containing any cpu you want to disable
> >> balancing on, otherwise some balancing will happen.
> > It won't be much of a balancing in this case because this just one cpu per
> > domain.
> > In other words no that's not how it supposed to work. There is code in
> > cpu_attach_domain() that is supposed to remove redundant levels
> > (sd_degenerate() stuff). There is an explicit check in there for numcpus == 1.
> > btw The reason you got a different result that I did is because you have a
> > NUMA box where is mine is UMA. I was able to reproduce the problem though by
> > enabling multi-core scheduler. In which case I also get one redundant domain
> > level CPU, with a single CPU in it.
> > So we definitely need to fix this. I'll try to poke around tomorrow and figure
> > out why redundant level is not dropped.
> > 
> 
> You were not using latest kernel, were you?
> 
> There was a bug in sd degenerate code, and it has already been fixed:
> 	http://lkml.org/lkml/2008/11/8/10

With the above patch added, we now see the results that Max is showing as far as individual root domains being created with a span of just their own cpu when sched_load_balance is turned off.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/