From: Vivek Goyal <vgoyal@redhat.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <jens.axboe@oracle.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Linux Memory Management List <linux-mm@kvack.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead
Date: Wed, 3 Feb 2010 10:24:59 -0500 [thread overview]
Message-ID: <20100203152454.GA17059@redhat.com> (raw)
In-Reply-To: <20100203062756.GB22890@localhost>
On Wed, Feb 03, 2010 at 02:27:56PM +0800, Wu Fengguang wrote:
> Vivek,
>
> On Wed, Feb 03, 2010 at 06:38:03AM +0800, Vivek Goyal wrote:
> > On Tue, Feb 02, 2010 at 11:28:35PM +0800, Wu Fengguang wrote:
> > > Andrew,
> > >
> > > This is to lift default readahead size to 512KB, which I believe yields
> > > more I/O throughput without noticeably increasing I/O latency for today's HDD.
> > >
> >
> > Hi Fengguang,
> >
> > I was doing a quick test with the patches. I was using fio to run some
> > sequential reader threads. I have got one access to one Lun from an HP
> > EVA. In my case it looks like with the patches throughput has come down.
>
> Thank you for the quick testing!
>
> This patchset does 3 things:
>
> 1) 512K readahead size
> 2) new readahead algorithms
> 3) new readahead tracing/stats interfaces
>
> (1) will impact performance, while (2) _might_ impact performance in
> case of bugs.
>
> Would you kindly retest the patchset with readahead size manually set
> to 128KB? That would help identify the root cause of the performance
> drop:
>
> DEV=sda
> echo 128 > /sys/block/$DEV/queue/read_ahead_kb
>
I have got two paths to the HP EVA and got multipath device setup(dm-3). I
noticed with vanilla kernel read_ahead_kb=128 after boot but with your patches
applied it is set to 4. So looks like something went wrong with device
size/capacity detection hence wrong defaults. Manually setting
read_ahead_kb=512, got me better performance as compare to vanilla kernel.
AVERAGE[bsr]
-------
job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us)
--- --- -- ------------ ----------- ------------- -----------
bsr 3 1 190302 97937.3 0 0
bsr 3 2 185636 223286 0 0
bsr 3 4 185986 363658 0 0
bsr 3 8 184352 428478 0 0
bsr 3 16 185646 594311 0 0
Thanks
Vivek
> The readahead stats provided by the patchset are very useful for
> analyzing the problem:
>
> mount -t debugfs none /debug
>
> # for each benchmark:
> echo > /debug/readahead/stats # reset counters
> # do benchmark
> cat /debug/readahead/stats # check counters
>
> Thanks,
> Fengguang
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next prev parent reply other threads:[~2010-02-03 15:24 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-02 15:28 [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead Wu Fengguang
2010-02-02 15:28 ` [PATCH 01/11] readahead: limit readahead size for small devices Wu Fengguang
2010-02-02 19:38 ` Jens Axboe
2010-02-03 6:13 ` Wu Fengguang
2010-02-03 8:23 ` Jens Axboe
2010-02-04 8:24 ` Clemens Ladisch
2010-02-04 13:00 ` Wu Fengguang
2010-02-02 15:28 ` [PATCH 02/11] readahead: bump up the default readahead size Wu Fengguang
2010-02-02 15:28 ` [PATCH 03/11] readahead: introduce {MAX|MIN}_READAHEAD_PAGES macros for ease of use Wu Fengguang
2010-02-02 15:28 ` [PATCH 04/11] readahead: replace ra->mmap_miss with ra->ra_flags Wu Fengguang
2010-02-02 15:28 ` [PATCH 05/11] readahead: retain inactive lru pages to be accessed soon Wu Fengguang
2010-02-02 15:28 ` [PATCH 06/11] readahead: thrashing safe context readahead Wu Fengguang
2010-02-02 15:28 ` [PATCH 07/11] readahead: record readahead patterns Wu Fengguang
2010-02-02 15:28 ` [PATCH 08/11] readahead: add tracing event Wu Fengguang
2010-02-12 16:19 ` Steven Rostedt
2010-02-14 3:56 ` Wu Fengguang
2010-02-02 15:28 ` [PATCH 09/11] readahead: add /debug/readahead/stats Wu Fengguang
2010-02-02 15:28 ` [PATCH 10/11] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
2010-02-02 17:39 ` Linus Torvalds
2010-02-02 18:13 ` Olivier Galibert
2010-02-02 18:40 ` Linus Torvalds
2010-02-02 18:48 ` Olivier Galibert
2010-02-02 19:14 ` Linus Torvalds
2010-02-02 19:59 ` david
2010-02-02 20:22 ` Linus Torvalds
2010-02-02 15:28 ` [PATCH 11/11] radixtree: speed up next/prev hole search Wu Fengguang
2010-02-02 22:38 ` [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead Vivek Goyal
2010-02-02 23:17 ` Vivek Goyal
2010-02-03 6:27 ` Wu Fengguang
2010-02-03 15:24 ` Vivek Goyal [this message]
2010-02-03 15:58 ` Vivek Goyal
2010-02-04 13:21 ` Wu Fengguang
2010-02-04 15:52 ` Vivek Goyal
2010-02-04 13:44 ` Wu Fengguang
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