Re: CFS scheduler OLTP perforamnce

[Peter Zijlstra <peterz@infradead.org>]

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?