linux-kernel - RE: CFS scheduler OLTP perforamnce

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Date:	Fri, 12 Dec 2008 10:25:47 -0700
From:	"Ma, Chinang" <chinang.ma@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	"Chilukuri, Harita" <harita.chilukuri@...el.com>,
	"Wang, Peter Xihong" <peter.xihong.wang@...el.com>,
	"Nueckel, Hubert" <hubert.nueckel@...el.com>
Subject: RE: CFS scheduler OLTP perforamnce



>-----Original Message-----
>From: Peter Zijlstra [mailto:peterz@...radead.org]
>Sent: Friday, December 12, 2008 4:12 AM
>To: Ma, Chinang
>Cc: Ingo Molnar; linux-kernel@...r.kernel.org; Wilcox, Matthew R; Van De
>Ven, Arjan; Styner, Douglas W; Chilukuri, Harita; Wang, Peter Xihong;
>Nueckel, Hubert
>Subject: Re: CFS scheduler OLTP perforamnce
>
>On Thu, 2008-12-11 at 16:25 -0700, Ma, Chinang wrote:
>> We are evaluating the CFS OLTP performance with 2.6.28-c7 kernel. In
>> this workload once a database foreground process commit a transaction
>> it will signal the log writer process to write to the log file.
>> Foreground processes will wait until log writer finish writing and
>> wake them up. With hundreds of foreground process running in the
>> system, it is important that the log writer get to run as soon as data
>> is available.
>>
>> Here are the experiments we have done with 2.6.28-rc7.
>> 1. Increase log writer priority "renice -20 <log writer pid>" while
>> keeping all other processes running in default CFS priority. We get a
>> baseline performance with log latency (scheduling + i/o) at 7 ms.
>
>Is this better or the same than nice-0 ?
>
>> 2. To reduce log latency, we set log writer to SCHED_RR with higher
>> priority. We tried "chrt -p 49  <log writer pid>" and got 0.7% boost
>> in performance with log latency reduced to 6.4 ms.
>>
>> It seems that in this case renice to higher priority with CFS did not
>> reduce scheduling latency as well as SCHED_RR.
>
>Is there a question in this email?
>

Can renice performance as well as SCHED_RR?

-Chinang
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