linux-kernel - Re: SSD and IO schedulers

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Date:	Wed, 8 Apr 2009 21:18:59 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	J.A. Magallón <jamagallon@....com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Cc:	Jan Knutar <jk-lkml@....fi>
Subject: Re: SSD and IO schedulers

Hi,
I found that elevator=deadline performs much better than noop for
writes, and almost as well for reads, and started to wonder how a
combination of noop (for read) + deadline (for write) would work in
practice (since deadline still doesn't support the automatic ssd
detection).
I developed a simple hybrid scheduler (see attached), that implements
this idea, and it saved 1 s of my boot time compared to all other
schedulers (cfq, deadline and noop, each loses on some part of the
workload), that is a mixed read write workload, with writes that go
mainly to a very slow device (SDHC card, where I mount /var).

This proof of concept still doesn't support priorities, but I'm
willing to add them at least for read, in which the latency for
sync-reads could be improved.

Corrado

On Sat, Feb 7, 2009 at 6:58 PM, Jan Knutar <jk-lkml@....fi> wrote:
> On Wednesday 04 February 2009, J.A. Magallón wrote:
>
>> Perhaps the reason is that, as the SSD is not so good, it behaves
>> more like a rotational drive ;).
>
> Do any other SSDs except Intel's exist that DON'T behave more like a
> rotational drive? I am guessing using something like LogFS would give
> the biggest boost on cheap SSDs and all memory cards.
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-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
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View attachment "ssd-iosched.c" of type "text/x-csrc" (10891 bytes)