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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>, Li Shaohua <shaohua.li@intel.com>
Subject: Re: Bad SSD performance with recent kernels
Date: Mon, 30 Jan 2012 22:48:21 +0800	[thread overview]
Message-ID: <20120130144821.GA23671@localhost> (raw)
In-Reply-To: <1327831380.14602.6.camel@edumazet-laptop>

On Sun, Jan 29, 2012 at 11:03:00AM +0100, Eric Dumazet wrote:

> Very strange, my bissection ended on following commit :
> 
> commit 805f6b5e1cbfedfb9b3d354013e7f4b13a79270f
> Author: Tao Ma <boyu.mt@taobao.com>
> Date:   Fri Mar 11 20:11:59 2011 +0100
> 
>     blktrace: Use rq->cmd_flags directly in blk_add_trace_rq.
> 
> This makes no sense.

Yeah, commit 55602dd66f535 ("fs: make generic file read/write
functions plug") looks like the real root cause and should probably
be reverted as a whole. Buffered read/write syscalls are not directly
tied to IO after all (readahead/writeback have the right plug points).

Thanks,
Fengguang

> hdparm uses 2MB block reads, so read_ahead (128KB) is too small for best
> perf
> 
> # cat /sys/class/block/sda/queue/read_ahead_kb
> 128
> 
> # dd if=/dev/sda of=/dev/null bs=128k 
> ^C
> 63744+0 enregistrements lus
> 63743+0 enregistrements écrits
> 8354922496 octets (8,4 GB) copiés, 39,975 s, 209 MB/s
> 
> # hdparm -t /dev/sda
> 
> /dev/sda:
>  Timing buffered disk reads: 510 MB in  3.00 seconds = 169.75 MB/sec
> 
> # uname -a
> Linux edumazet-laptop 3.0.0-15-generic #26-Ubuntu SMP Fri Jan 20
> 17:23:00 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
> 
> 

  parent reply	other threads:[~2012-01-31  0:13 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
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 [this message]
2012-01-28 17:01   ` Herbert Poetzl

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