linux-kernel - Re: Low latency I/O scheduling

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Date:	Sat, 20 Jun 2009 00:26:27 +0300
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: Low latency I/O scheduling

On Mon, 2009-06-08 at 19:40 +0200, Corrado Zoccolo wrote:
> Hi,
> sometime ago on the mailing list, the issue of too high latencies
> introduced by I/O scheduling was raised.
> I've done some study, and identified a way to improve on workloads
> that have >1 random readers.

You can say that again....

While there was all the fuzz about CPU scheduler, just doing some heavy
IO can literally stall the system for minutes (and I am not talking
about swap trashing, I have here 2 GB, and about 400 MB used)


Sometimes it goes so far, that I have to suspend the offending process.
I mostly compile stuff, buf file copies have even worse effect.


I tried CFQ, AS, and didn't see much difference
(but ionice on CFQ really helps)

Best regards,
	Maxim Levitsky

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