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Re: Linux I/O tuning: CFQ vs. deadline

From: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: "Greg Smith *EXTERN*" <greg(at)2ndquadrant(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Date: 2010-02-08 14:57:25
Message-ID: D960CB61B694CF459DCFB4B0128514C203938157@exadv11.host.magwien.gv.at (view raw or flat)
Thread:
Lists: pgsql-performance
Greg Smith wrote:
> Recently I've made a number of unsubstantiated claims that the deadline 
> scheduler on Linux does bad things compared to CFQ when running 
> real-world mixed I/O database tests.  Unfortunately every time I do one 
> of these I end up unable to release the results due to client 
> confidentiality issues.  However, I do keep an eye out for people who 
> run into the same issues in public benchmarks, and I just found one:  
> http://insights.oetiker.ch/linux/fsopbench/

That is interesting; particularly since I have made one quite different
experience in which deadline outperformed CFQ by a factor of approximately 4.

So I tried to look for differences, and I found two possible places:
- My test case was read-only, our production system is read-mostly.
- We did not have a RAID array, but a SAN box (with RAID inside).

The "noop" scheduler performed about as well as "deadline".
I wonder if the two differences above could explain the different
result.

Yours,
Laurenz Albe

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Next:From: Kevin GrittnerDate: 2010-02-08 15:24:56
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Previous:From: Greg SmithDate: 2010-02-08 09:45:10
Subject: Linux I/O tuning: CFQ vs. deadline

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