From: Peter Zijlstra <peterz@infradead.org>
To: David Rees <drees76@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Large write = large latency for small writes
Date: Tue, 17 Mar 2009 23:09:12 +0100 [thread overview]
Message-ID: <1237327752.5189.1119.camel@laptop> (raw)
In-Reply-To: <72dbd3150903171319u567fc267m36857506c024315d@mail.gmail.com>
On Tue, 2009-03-17 at 13:19 -0700, David Rees wrote:
> I have a simple test case which demonstrates the huge increase in
> write latency that occurs for small writes when a large disk
> saturating write is also in progress [3]:
>
> dd if=/dev/zero of=/tmp/bigfile bs=1M count=10000 conv=fdatasync &
> sleep 10
> time dd if=/dev/zero of=/tmp/smallfile bs=4k count=1 conv=fdatasync
>
> On a handful of systems I have access to, it took anywhere from 6-45
> seconds for the small write to complete. Others in the bug have
> reproduced this across a number of filesystems (ext3, reiserfs, ext4).
> xfs in particular seems to handle this test case better than the
> others. As do systems which can sustain high write speeds.
How does it fare without the fdatasync?
That is, is it the sync that's taking ages, or the ditry?
next prev parent reply other threads:[~2009-03-17 22:10 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-17 20:19 Large write = large latency for small writes David Rees
2009-03-17 22:09 ` Peter Zijlstra [this message]
2009-03-17 22:29 ` David Rees
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