From: Andrew Morton <akpm@linux-foundation.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: hifumi.hisashi@oss.ntt.co.jp, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, kosaki.motohiro@jp.fujitsu.com,
linux-mm@kvack.org, jens.axboe@oracle.com
Subject: Re: [PATCH] readahead:add blk_run_backing_dev
Date: Tue, 26 May 2009 16:42:52 -0700 [thread overview]
Message-ID: <20090526164252.0741b392.akpm@linux-foundation.org> (raw)
In-Reply-To: <20090522023323.GA10864@localhost>
On Fri, 22 May 2009 10:33:23 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:
> > I tested above patch, and I got same performance number.
> > I wonder why if (PageUptodate(page)) check is there...
>
> Thanks! This is an interesting micro timing behavior that
> demands some research work. The above check is to confirm if it's
> the PageUptodate() case that makes the difference. So why that case
> happens so frequently so as to impact the performance? Will it also
> happen in NFS?
>
> The problem is readahead IO pipeline is not running smoothly, which is
> undesirable and not well understood for now.
The patch causes a remarkably large performance increase. A 9%
reduction in time for a linear read? I'd be surprised if the workload
even consumed 9% of a CPU, so where on earth has the kernel gone to?
Have you been able to reproduce this in your testing?
Thanks.
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next prev parent reply other threads:[~2009-05-26 23:42 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-18 9:38 [PATCH] readahead:add blk_run_backing_dev Hisashi Hifumi
2009-05-18 17:53 ` Jens Axboe
2009-05-19 0:44 ` Hisashi Hifumi
2009-05-19 10:05 ` Hisashi Hifumi
2009-05-20 0:55 ` Hisashi Hifumi
2009-05-20 2:51 ` Wu Fengguang
2009-05-21 6:01 ` Hisashi Hifumi
2009-05-22 1:05 ` Wu Fengguang
2009-05-22 1:44 ` Hisashi Hifumi
2009-05-22 2:33 ` Wu Fengguang
2009-05-26 23:42 ` Andrew Morton [this message]
2009-05-27 0:25 ` Hisashi Hifumi
2009-05-27 2:09 ` Wu Fengguang
2009-05-27 2:21 ` Hisashi Hifumi
2009-05-27 2:35 ` KOSAKI Motohiro
2009-05-27 2:36 ` Andrew Morton
2009-05-27 2:38 ` Hisashi Hifumi
2009-05-27 3:55 ` Wu Fengguang
2009-05-27 4:06 ` KOSAKI Motohiro
2009-05-27 4:36 ` Wu Fengguang
2009-05-27 6:20 ` Hisashi Hifumi
2009-05-28 1:20 ` Hisashi Hifumi
2009-05-28 2:23 ` KOSAKI Motohiro
2009-06-01 1:39 ` Hisashi Hifumi
2009-06-01 2:23 ` KOSAKI Motohiro
2009-05-27 2:36 ` Wu Fengguang
2009-05-27 2:47 ` Hisashi Hifumi
2009-05-27 2:57 ` Wu Fengguang
2009-05-27 3:06 ` Hisashi Hifumi
2009-05-27 3:26 ` KOSAKI Motohiro
2009-06-01 2:37 ` Wu Fengguang
2009-06-01 2:51 ` Hisashi Hifumi
2009-06-01 3:02 ` Wu Fengguang
2009-06-01 3:06 ` KOSAKI Motohiro
2009-06-01 3:07 ` Hisashi Hifumi
2009-06-01 4:30 ` Wu Fengguang
2009-05-27 2:07 ` Wu Fengguang
2009-05-20 1:07 ` KOSAKI Motohiro
2009-05-20 1:43 ` Hisashi Hifumi
2009-05-20 2:52 ` Wu Fengguang
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