Date: Mon, 13 Oct 2008 23:39:33 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Grant Grundler" <grundler@google.com>
Cc: "kenneth johansson" <ken@kenjo.org>, linux-ide@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: weird throughput on write to SATA disk
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On Mon, 13 Oct 2008 14:07:15 -0700
"Grant Grundler" <grundler@google.com> wrote:

> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <ken@kenjo.org> wrote:
> > When writing data to /dev/sdb (that is the whole disk and no filesystem)
> > it starts out ok around 100MB/sec but soon end up doing considerably
> > worse. For prolonged times lasting several minutes it hovers in the
> > 20-30MB/sec.
> 
> Is the application using "O_DIRECT"?
> If not, could be issue with how VM writeback is (not) working.

Or just mashing up the I/O horribly. Would also be worth turning the CFQ
scheduler off or applying Arjan van de Ven's patches to fix the ioprio of
the kernel writeout threads. That last patch makes a huge difference here.

Alan
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