linux-kernel - Re: RT sched: cpupri_vec lock contention with def_root

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Message-ID: <20081119202109.GA2383@sgi.com>
Date:	Wed, 19 Nov 2008 14:21:09 -0600
From:	Dimitri Sivanich <sivanich@....com>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	Gregory Haskins <ghaskins@...ell.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: RT sched: cpupri_vec lock contention with def_root_domain and no load balance

On Wed, Nov 19, 2008 at 12:17:38PM -0800, Max Krasnyansky wrote:
> 
> 
> Dimitri Sivanich wrote:
> > On Wed, Nov 19, 2008 at 11:49:36AM -0800, Max Krasnyansky wrote:
> >> I think the idea is that we want to make balancer a noop on those processors.
> > 
> > Ultimately, making the balancer a noop on processors with load balancing turned off would be the best solution.
> Yes. I forgot to point out that if we do change cpusets to generate sched
> domain per cpu we want to make sure that balancer is still a noop just like it
> is today with the null sched domain.

Sorry, I meant root_domain per cpu, not sched domain.  Having NULL sched domains for these cpus is fine.

> 
> >> We could change cpusets code to create a root sched domain for each cpu I
> >> guess. But can we maybe scale cpupri some other way ?
> > 
> > It doesn't make sense to me that they'd have a root domain attached that spans more of the the system than that cpu.
> I think 'root' in this case is a bit of a misnomer. What I meant is that each
> non-balanced cpu would be in a separate sched domain.

I think a NULL sched domain, as it is now, is fine.
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