From: Wu Fengguang <wfg@linux.intel.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>,
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 00:10:58 +0800 [thread overview]
Message-ID: <20120129161058.GA13156@localhost> (raw)
In-Reply-To: <1327842831.2718.2.camel@edumazet-laptop>
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?
Thanks,
Fengguang
next prev parent reply other threads:[~2012-01-29 16:21 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 [this message]
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
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
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