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Subject: Re: CFS scheduler OLTP perforamnce
From: Peter Zijlstra <peterz@infradead.org>
To: "Ma, Chinang" <chinang.ma@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "Wilcox, Matthew R" <matthew.r.wilcox@intel.com>,
       "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
       "Styner, Douglas W" <douglas.w.styner@intel.com>,
       "Chilukuri, Harita" <harita.chilukuri@intel.com>,
       "Wang, Peter Xihong" <peter.xihong.wang@intel.com>,
       "Nueckel, Hubert" <hubert.nueckel@intel.com>
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References: <BC02C49EEB98354DBA7F5DD76F2A9E80030A74A5FF@azsmsx501.amr.corp.intel.com>
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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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