From: Shaohua Li <shaohua.li@intel.com>
To: Herbert Poetzl <herbert@13thfloor.at>
Cc: Wu Fengguang <wfg@linux.intel.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
Tejun Heo <tj@kernel.org>
Subject: Re: Bad SSD performance with recent kernels
Date: Mon, 30 Jan 2012 16:12:22 +0800 [thread overview]
Message-ID: <1327911142.21268.7.camel@sli10-conroe> (raw)
In-Reply-To: <20120130073621.GN29272@MAIL.13thfloor.at>
On Mon, 2012-01-30 at 08:36 +0100, Herbert Poetzl wrote:
> On Mon, Jan 30, 2012 at 03:22:38PM +0800, Shaohua Li wrote:
> > On Mon, 2012-01-30 at 08:13 +0100, Herbert Poetzl wrote:
> >> On Mon, Jan 30, 2012 at 11:17:38AM +0800, Shaohua Li wrote:
> >>> 2012/1/30 Wu Fengguang <wfg@linux.intel.com>:
> >>>> On Sun, Jan 29, 2012 at 02:13:51PM +0100, Eric Dumazet wrote:
> >>>>> Le dimanche 29 janvier 2012 à 19:16 +0800, Wu Fengguang a écrit :
>
> >>>>>> Note that as long as buffered read(2) is used, it makes almost no
> >>>>>> difference (well, at least for now) to do "dd bs=128k" or "dd bs=2MB":
> >>>>>> the 128kb readahead size will be used underneath to submit read IO.
>
> >>>>> Hmm...
>
> >>>>> # echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=128k count=32768
> >>>>> 32768+0 enregistrements lus
> >>>>> 32768+0 enregistrements écrits
> >>>>> 4294967296 octets (4,3 GB) copiés, 20,7718 s, 207 MB/s
>
>
> >>>>> # echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=2M count=2048
> >>>>> 2048+0 enregistrements lus
> >>>>> 2048+0 enregistrements écrits
> >>>>> 4294967296 octets (4,3 GB) copiés, 27,7824 s, 155 MB/s
>
> >>>> Interesting. Here are my test results:
>
> >>>> root@lkp-nex04 /home/wfg# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=128k count=32768
> >>>> 32768+0 records in
> >>>> 32768+0 records out
> >>>> 4294967296 bytes (4.3 GB) copied, 19.0121 s, 226 MB/s
> >>>> root@lkp-nex04 /home/wfg# echo 3 >/proc/sys/vm/drop_caches ;dd if=/dev/sda of=/dev/null bs=2M count=2048
> >>>> 2048+0 records in
> >>>> 2048+0 records out
> >>>> 4294967296 bytes (4.3 GB) copied, 19.0214 s, 226 MB/s
>
> >>>> Maybe the /dev/sda performance bug on your machine is sensitive to timing?
> >>> I got similar result:
> >>> 128k: 224M/s
> >>> 1M: 182M/s
>
> >>> 1M block size is slow, I guess it's CPU related.
>
> >>> And as for the big regression with newer kernel than 2.6.38,
> >>> please check if idle=poll helps. CPU idle dramatically impacts
> >>> disk performance and even latest cpuidle governor doesn't help
> >>> for some CPUs.
>
> >> here are the tests with idle=poll and after switching to 128k
> >> (instead of 1M) blocksize (same amount of data transferred)
>
> >> kernel ------------ read /dev/sda -------------
> >> --- noop --- - deadline - ---- cfs ---
> >> [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU
> >> --------------------------------------------------
> >> 3.2.2 45.82 3.7 44.85 3.6 45.04 3.4
> >> 3.2.2i 45.59 2.3 51.78 2.6 46.03 2.2
> >> 3.2.2i128 250.24 20.9 252.68 21.3 250.00 21.6
>
> >> kernel -- write --- ------------------read -----------------
> >> --- noop --- --- noop --- - deadline - ---- cfs ---
> >> [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU [MB/s] %CPU
> >> ----------------------------------------------------------------
> >> 3.2.2 270.95 42.6 162.36 9.9 162.63 9.9 162.65 10.1
> >> 3.2.2i 269.10 41.4 170.82 6.6 171.20 6.6 170.91 6.7
> >> 3.2.2i128 270.38 67.7 162.35 10.2 163.01 10.3 162.34 10.7
>
> > What's 3.2.2i and 3.2.2i128?
>
> 3.2.2 ...... kernel with default options (bs=1M)
> 3.2.2i ..... kernel with idle=poll (bs=1M)
> 3.2.2i128 .. kernel with idle=poll (bs=128k)
>
> > does idle=poll help?
>
> doesn't look like, at least to me ...
what's your /sys/block/sdx/queue/max_sectors_kb? if you make it smaller,
does the performance increase? In my system, a smaller max_sectors_kb
makes bs=2M and bs=128k have similar performance, which makes me think
it's CPU doesn't catch up quickly after a request finishes.
next prev parent reply other threads:[~2012-01-30 8:13 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 6:00 Bad SSD performance with recent kernels Herbert Poetzl
2012-01-27 6:44 ` Eric Dumazet
2012-01-28 12:51 ` Wu Fengguang
2012-01-28 13:33 ` Eric Dumazet
2012-01-29 5:59 ` Wu Fengguang
2012-01-29 8:42 ` Herbert Poetzl
2012-01-29 9:28 ` Wu Fengguang
2012-01-29 10:03 ` Eric Dumazet
2012-01-29 11:16 ` Wu Fengguang
2012-01-29 13:13 ` Eric Dumazet
2012-01-29 15:52 ` Pádraig Brady
2012-01-29 16:10 ` Wu Fengguang
2012-01-29 20:15 ` Herbert Poetzl
2012-01-30 11:18 ` Wu Fengguang
2012-01-30 12:34 ` Eric Dumazet
2012-01-30 14:01 ` Wu Fengguang
2012-01-30 14:05 ` Wu Fengguang
2012-01-30 3:17 ` Shaohua Li
2012-01-30 5:31 ` Eric Dumazet
2012-01-30 5:45 ` Shaohua Li
2012-01-30 7:13 ` Herbert Poetzl
2012-01-30 7:22 ` Shaohua Li
2012-01-30 7:36 ` Herbert Poetzl
2012-01-30 8:12 ` Shaohua Li [this message]
2012-01-30 10:31 ` Shaohua Li
2012-01-30 14:28 ` Wu Fengguang
2012-01-30 14:51 ` Eric Dumazet
2012-01-30 22:26 ` Vivek Goyal
2012-01-31 0:14 ` Shaohua Li
2012-01-31 1:07 ` Wu Fengguang
2012-01-31 3:00 ` Shaohua Li
2012-01-31 2:17 ` Eric Dumazet
2012-01-31 8:46 ` Eric Dumazet
2012-01-31 6:36 ` Herbert Poetzl
2012-01-30 14:48 ` Wu Fengguang
2012-01-28 17:01 ` Herbert Poetzl
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1327911142.21268.7.camel@sli10-conroe \
--to=shaohua.li@intel.com \
--cc=akpm@linux-foundation.org \
--cc=axboe@kernel.dk \
--cc=eric.dumazet@gmail.com \
--cc=herbert@13thfloor.at \
--cc=linux-kernel@vger.kernel.org \
--cc=tj@kernel.org \
--cc=wfg@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).