linux-kernel - Re: sched: Avoid SMT siblings in select_idle

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Message-ID: <20120223111929.GA23646@elte.hu>
Date:	Thu, 23 Feb 2012 12:19:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <peterz@...radead.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>
Subject: Re: sched: Avoid SMT siblings in select_idle_sibling() if possible


* Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> wrote:

> * Mike Galbraith <efault@....de> [2012-02-20 19:14:21]:
> 
> > > I was looking at this code due to vatsa wanting to do SD_BALANCE_WAKE.
> > 
> > I really really need to find time to do systematic mainline testing.
> > 
> > Enabling SD_BALANCE_WAKE used to be decidedly too expensive to consider.
> > Maybe that has changed, but I doubt it.  (general aside: testing with a
> > bloated distro config is a big mistake)
> 
> I am seeing 2.6% _improvement_ in volanomark score by enabling SD_BALANCE_WAKE 
> at SMT/MC domains.
> 
> Machine : 2 Quad-core Intel X5570 CPU (H/T enabled)
> Kernel  : tip (HEAD at 6241cc8)
> Java	: OpenJDK 1.6.0_20
> Volano  : 2_9_0
> 
> Volano benchmark was run 4 times with and w/o SD_BALANCE_WAKE enabled in
> SMT/MC domains.
> 
> 				Average score	std. dev
> 
> SD_BALANCE_WAKE disabled	369459.750	4825.046
> SD_BALANCE_WAKE enabled		379070.500	379070.5
> 
> I am going to try pipe benchmark next. Do you have suggestions 
> for any other benchmarks I should try to see the effect of 
> SD_BALANCE_WAKE turned on in SMT/MC domains?

sysbench is one of the best ones punishing bad scheduler 
balancing mistakes.

Thanks,

	Ingo
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