linux-kernel - Re: Disk schedulers

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Message-Id: <1203095486.6663.12.camel@localhost>
Date:	Fri, 15 Feb 2008 10:11:26 -0700
From:	Zan Lynx <zlynx@....org>
To:	Prakash Punnoor <prakash@...noor.de>
Cc:	Jan Engelhardt <jengelh@...putergmbh.de>,
	Lukas Hejtmanek <xhejtman@....muni.cz>,
	linux-kernel@...r.kernel.org
Subject: Re: Disk schedulers


On Fri, 2008-02-15 at 15:57 +0100, Prakash Punnoor wrote:
> On the day of Friday 15 February 2008 Jan Engelhardt hast written:
> > On Feb 14 2008 17:21, Lukas Hejtmanek wrote:
> > >Hello,
> > >
> > >whom should I blame about disk schedulers?
> >
> > Also consider
> > - DMA (e.g. only UDMA2 selected)
> > - aging disk
> 
> Nope, I also reported this problem _years_ ago, but till now much hasn't 
> changed. Large writes lead to read starvation.

Yes, I see this often myself.  It's like the disk IO queue (I set mine
to 1024) fills up, and pdflush and friends can stuff write requests into
it much more quickly than any other programs can provide read requests.

CFQ and ionice work very well up until iostat shows average IO queuing
above 1024 (where I set the queue number).
-- 
Zan Lynx <zlynx@....org>

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