linux-kernel - Re: CFS scheduler OLTP perforamnce

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Date:	Fri, 12 Dec 2008 13:12:13 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Ma, Chinang" <chinang.ma@...el.com>
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

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?


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