linux-kernel - Re: ext4 data=writeback performs worse than data=ordered now

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Date:	Wed, 14 Dec 2011 22:03:05 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Cc:	Jan Kara <jack@...e.cz>, Li Shaohua <shaohua.li@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: ext4 data=writeback performs worse than data=ordered now

On Wed, Dec 14, 2011 at 10:00:25PM +0800, Wu Fengguang wrote:
> > The worst case happens for the USB key, where both old/new kernels
> > see ~10% worse performance for data=writeback.
> 
> >                     ext4                   ext4:wb
> > ------------------------  ------------------------
> >                     6.20       -10.6%         5.54  fat/UKEY-thresh=100M/ext4-1dd-1-3.2.0-rc3-pause6+
> 
> Some more comparison numbers for the above worst case.
> 
> I don't see obvious differences from the balance_dirty_pages graphs,

Ah there seem to be many more blocks in write_begin(), indicated by
the more negative pause times in the attached second graph.

Thanks,
Fengguang


Download attachment "balance_dirty_pages-pause.png" of type "image/png" (38991 bytes)

Download attachment "balance_dirty_pages-pause.png" of type "image/png" (53241 bytes)