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

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Date:	Thu, 23 Feb 2012 16:50:05 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>
Subject: Re: sched: Avoid SMT siblings in select_idle_sibling() if possible

* Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> [2012-02-23 16:19:59]:

> > 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.

Ditto with pipe benchmark.

> Machine : 2 Quad-core Intel X5570 CPU (H/T enabled)
> Kernel  : tip (HEAD at 6241cc8)

"perf bench sched pipe" was run 10 times and average ops/sec score
alongwith std. dev is noted as below.


		SD_BALANCE_WAKE		SD_BALANCE_WAKE
		 disabled		enabled

Avg. score	108984.900 		111844.300 (+2.6%)
std dev		20383.457		21668.604

Note:

SD_BALANCE_WAKE for SMT/MC domain was enabled by writing into appropriate 
flags file present in /proc:

	# cd /proc/sys/kernel/sched_domain/
	# for i in `find . -name flags | grep domain1`; do echo 4671 > $i; done
	# for i in `find . -name flags | grep domain0`; do echo 703 > $i; done

- vatsa

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