Re: ext4 data=writeback performs worse than data=ordered now

[Wu Fengguang]

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

Attachment: balance_dirty_pages-pause.png
Description: PNG image

Attachment: balance_dirty_pages-pause.png
Description: PNG image