linux-kernel - Re: Bad SSD performance with recent kernels

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Message-ID: <20120129055917.GB8513@localhost>
Date:	Sun, 29 Jan 2012 13:59:17 +0800
From:	Wu Fengguang <wfg@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Herbert Poetzl <herbert@...hfloor.at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Subject: Re: Bad SSD performance with recent kernels

On Sat, Jan 28, 2012 at 02:33:31PM +0100, Eric Dumazet wrote:
> Le samedi 28 janvier 2012 à 20:51 +0800, Wu Fengguang a écrit :
> 
> > Would you please create a filesystem and large file on sda and run the
> > tests on the file? There was some performance bug on reading the raw
> > /dev/sda device file..
> 
> Hmm... latest kernel has the performance bug right now.
> 
> Really if /dev/sda is slow, we are stuck.

What's the block size? If it's < 4k, performance might be hurt.

        blockdev --getbsz /dev/sda

> FYI, I started a bisection.

Thank you! If the bisection would take much human time, it should be
easier to collect some blktrace data on reading /dev/sda for analyzes.

Thanks,
Fengguang
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