linux-kernel - Re: scheduler scalability - cgroups, cpusets and load-balancing

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Message-ID: <20080129123223.GM1044@linux.vnet.ibm.com>
Date:	Tue, 29 Jan 2008 18:02:23 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Paul Jackson <pj@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steve Grubb <sgrubb@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	"Li, Tong N" <tong.n.li@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Menage <menage@...gle.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: scheduler scalability - cgroups, cpusets and load-balancing

On Tue, Jan 29, 2008 at 11:57:22AM +0100, Peter Zijlstra wrote:
> On Tue, 2008-01-29 at 10:53 +0100, Peter Zijlstra wrote:
> 
> > My thoughts were to make stronger use of disjoint cpu-sets. cgroups and
> > cpusets are related, in that cpusets provide a property to a cgroup.
> > However, load_balance_monitor()'s interaction with sched domains
> > confuses me - it might DTRT, but I can't tell.
> > 
> > [ It looks to me it balances a group over the largest SD the current cpu
> >   has access to, even though that might be larger than the SD associated
> >   with the cpuset of that particular cgroup. ]
> 
> Hmm, with a bit more thought I think that does indeed DTRT. Because, if
> the cpu belongs to a disjoint cpuset, the highest sd (with
> load-balancing enabled) would be that. Right?

Hi Peter,
	Yes, I was having this in mind when I wrote the load_balance_monitor() 
function - to only balance across cpus that form a disjoint cpuset in the 
system.

> [ Just a bit of a shame we have all cgroups represented on each cpu. ]

After reading your explanation in the other mail abt what you mean here,
I agree. Your suggestion to remove/add cfs_rq from/to the leaf_cfs_rq_list
upon dequeue_of_last_task/enqueue_of_first_task  AND

> Also, might be a nice idea to split the daemon up if there are indeed
> disjoint sets - currently there is only a single daemon which touches
> the whole system.

the above suggestions seems like good ideas. I can also look at reducing
the frequency at which the thread runs ..

-- 
Regards,
vatsa
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