Re: [PATCH 0/11] Per-bdi writeback flusher threads v9

Zhang, Yanmin
2009-06-05T01:14:47Z

On Thu, 2009-06-04 at 17:20 +0200, Frederic Weisbecker wrote:
> Hi,
>
>
> On Thu, May 28, 2009 at 01:46:33PM +0200, Jens Axboe wrote:
> > Hi,
> >
> > Here's the 9th version of the writeback patches. Changes since v8:

> I've just tested it on UP in a single disk.
>
> I've run two parallels dbench tests on two partitions and
> tried it with this patch and without.
I also tested V9 with multiple-dbench workload by starting multiple
dbench tasks and every task has 4 processes to do I/O on one partition (file
system). Mostly I use JBODs which have 7/11/13 disks.

I didn't find result regression between ﻿vanilla and V9 kernel on this workload.

>
> I used 30 proc each during 600 secs.
>
> You can see the result in attachment.
> And also there:
>
> http://kernel.org/pub/linux/kernel/people/frederic/dbench.pdf
> http://kernel.org/pub/linux/kernel/people/frederic/bdi-writeback-hda1.log
> http://kernel.org/pub/linux/kernel/people/frederic/bdi-writeback-hda3.log
> http://kernel.org/pub/linux/kernel/people/frederic/pdflush-hda1.log
> http://kernel.org/pub/linux/kernel/people/frederic/pdflush-hda3.log
>
>
> As you can see, bdi writeback is faster than pdflush on hda1 and slower
> on hda3. But, well that's not the point.
>
> What I can observe here is the difference on the standard deviation
> for the rate between two parallel writers on a same device (but
> two different partitions, then superblocks).
>
> With pdflush, the distributed rate is much better balanced than
> with bdi writeback in a single device.
>
> I'm not sure why. Is there something in these patches that makes
> several bdi flusher threads for a same bdi not well balanced
> between them?
>
> Frederic.