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

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Message-ID: <20120223121825.GC8454@linux.vnet.ibm.com>
Date:	Thu, 23 Feb 2012 17:48:25 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
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

* Ingo Molnar <mingo@...e.hu> [2012-02-23 12:19:29]:

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

Here are the sysbench oltp score on same machine i.e:

Machine : 2 Quad-core Intel X5570 CPU (H/T enabled)
Kernel  : tip (HEAD at 6241cc8)
sysbench : 0.4.12

sysbench was run with 16 threads as:

./sysbench --num-threads=16 --max-requests=100000 --test=oltp --oltp-table-size=500000 --mysql-socket=/var/lib/mysql/mysql.sock --oltp-read-only --mysql-user=root --mysql-password=blah run

sysbench was run 5 times with fs-cache being purged before each run
(echo 3 > /proc/sys/vm/drop_caches).

Average of 5 runs alongwith % std. dev. is noted for various OLTP stats

				SD_BALANCE_WAKE		SD_BALANCE_WAKE	
				disabled		enabled

transactions (per sec)		4833.826 (+- 0.75%)	4837.354 (+- 1%)
read/write requests (per sec)	67673.580 (+- 0.75%)	67722.960 (+- 1%)
other ops (per sec)		9667.654 (+- 0.75%)	9674.710 (+- 1%)

There is minor improvement seen when SD_BALANCE_WAKE is enabled at SMT/MC
domains, but no degradation observed with it enabled.

- vatsa

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