linux-kernel - Re: [PATCH] readahead:add blk_run_backing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 26 May 2009 19:36:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>
Subject: Re: [PATCH] readahead:add blk_run_backing_dev

On Wed, 27 May 2009 11:21:53 +0900 Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp> wrote:

> 
> At 11:09 09/05/27, Wu Fengguang wrote:
> >On Wed, May 27, 2009 at 08:25:04AM +0800, Hisashi Hifumi wrote:
> >> 
> >> At 08:42 09/05/27, Andrew Morton wrote:
> >> >On Fri, 22 May 2009 10:33:23 +0800
> >> >Wu Fengguang <fengguang.wu@...el.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
> >> 
> >> Hi Andrew.
> >> Yes, I tested this with dd.
> >> 
> >> >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?
> >> 
> >> Yes, this test on my environment is reproducible.
> >
> >Hisashi, does your environment have some special configurations?
> 
> Hi.
> My testing environment is as follows:
> Hardware: HP DL580 
> CPU:Xeon 3.2GHz *4 HT enabled
> Memory:8GB
> Storage: Dothill SANNet2 FC (7Disks RAID-0 Array)
> 
> I did dd to this disk-array and got improved performance number.
> 
> I noticed that when a disk is just one HDD, performance improvement
> is very small.
> 

Ah.  So it's likely to be some strange interaction with the RAID setup.

I assume that you're using the SANNet 2's "hardware raid"?  Or is the
array set up as jbod and you're using kernel raid0?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/