linux-kernel - RE: 2.6.27-rc5 OLTP performance regression

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Message-ID: <BC02C49EEB98354DBA7F5DD76F2A9E8002FEC1730D@azsmsx501.amr.corp.intel.com>
Date:	Thu, 25 Sep 2008 14:04:01 -0700
From:	"Ma, Chinang" <chinang.ma@...el.com>
To:	"Ma, Chinang" <chinang.ma@...el.com>, Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Gregory Haskins <ghaskins@...ell.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"Tripathi, Sharad C" <sharad.c.tripathi@...el.com>,
	"Chilukuri, Harita" <harita.chilukuri@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: 2.6.27-rc5 OLTP performance regression

We also tested sched_shares_ratelimit = 100 ms and reduce the OLTP regression to 0.2%. (very small return in performance with 10x the value). Can we count on this sched_shares_ratelimit tunable be always accessible for workload that does not depend on group fairness?

Chinang

-----Original Message-----
From: Ma, Chinang
Sent: Wednesday, September 10, 2008 5:08 PM
To: Ingo Molnar
Cc: Peter Zijlstra; Srivatsa Vaddagiri; Mike Galbraith; Gregory Haskins; Steven Rostedt; Nick Piggin; Siddha, Suresh B; Wilcox, Matthew R; Tripathi, Sharad C; Chilukuri, Harita; linux-kernel@...r.kernel.org
Subject: RE: 2.6.27-rc5 OLTP performance regression

When set to 10 ms the regression is about 0.4%. We get most of the 2%.

Chinang
-----Original Message-----
From: Ingo Molnar [mailto:mingo@...e.hu]
Sent: Wednesday, September 10, 2008 10:35 AM
To: Ma, Chinang
Cc: Peter Zijlstra; Srivatsa Vaddagiri; Mike Galbraith; Gregory Haskins; Steven Rostedt; Nick Piggin; Siddha, Suresh B; Wilcox, Matthew R; Tripathi, Sharad C; Chilukuri, Harita; linux-kernel@...r.kernel.org
Subject: Re: 2.6.27-rc5 OLTP performance regression


* Ma, Chinang <chinang.ma@...el.com> wrote:

> I increased the /proc/sys/kernel/sched_shares_ratelimit from 1
> millisecond to one second to reduce the frequency of shares update.
> That was okay for OLTP workload. As Peter mentioned, a larger value
> will reduce the accuracy of SMP fairness for group scheduler and the
> ratelimit and using a larger default value may not be good for general
> case.

does 10 msecs already get you most of the 2%? 1000 millisecond sounds
very (and probably unacceptable) coarse.

        Ingo
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