Message-ID: <50EEE3F5.7070405@optionshouse.com>
Date: Thu, 10 Jan 2013 09:53:25 -0600
From: Shaun Thomas <sthomas@optionshouse.com>
Reply-To: <sthomas@optionshouse.com>
Organization: Peak6
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To: Henri Philipps <henri.philipps@gmail.com>
CC: <pgsql-performance@postgresql.org>
Subject: Re: Two Necessary Kernel Tweaks for Linux Systems
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On 01/10/2013 02:51 AM, Henri Philipps wrote:

> http://research.cs.wisc.edu/adsl/Publications/meehean-thesis11.pdf

Wow, that was pretty interesting. It looks like for servers, the O(1) 
scheduler is much better even with the assignment bug he identified, and 
BFS responds better to varying load than CFS.

It's too bad the paper is so old and only considers the 2.6 kernel. I'd 
love to see this type of research applied to the latest.

> sched_latency_ns
> sched_min_granularity_ns
>
> I guess that higher numbers could improve performance too on systems
> with many cores and many connections.

I messed around with these a bit. Settings 10x smaller and 10x larger 
didn't do anything appreciable that I noticed. Performance metrics were 
within variance of my earlier tests. Only autogrouping and migration 
cost had any appreciable effect.

I'm glad we weren't the only ones who ran into this, too. You settled on 
a much higher setting than we did, but the end result was the same. I 
wonder how prevalent this will become as more servers are switched over 
to newer kernels in the next couple of years. Hopefully more people 
start complaining so they fix it. :)

-- 
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com

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