linux-ext4 - Re: [PATCH 1/2] ext2: speed up file creates by optimizing rec

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Message-ID: <4D003B5A.5060807@redhat.com>
Date:	Wed, 08 Dec 2010 20:13:46 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 1/2] ext2: speed up file creates by optimizing rec_len
 functions

On 12/8/10 3:44 PM, Andreas Dilger wrote:
> On 2010-12-08, at 14:07, Eric Sandeen wrote:
>> On 12/08/2010 01:01 PM, Andreas Dilger wrote:
>>> I think an important factor here is that this is being tested on
>>> a ramdisk, and is likely CPU bound, so any CPU reduction will
>>> directly be measured as a performance improvement.  Probably
>>> oprofile is in order to see where other major CPU users are.
>> 
>> Yep, I ran oprofile.
>> 
>> samples  %        app name                 symbol name 1140046
>> 41.8702  ext2.ko                  ext2_find_entry 1052117  38.6408
>> ext2.ko                  ext2_add_link 98424     3.6148  vmlinux
>> native_safe_halt 40461     1.4860  vmlinux
>> wait_on_page_read 29084     1.0682  vmlinux
>> find_get_page
>> 
>> pretty slammed on those 2 ext2 functions!  I think it's pretty 
>> overwhelmed by the linear search.
> 
> Can you test ext4 with nojournal mode, but with dir_index enabled?  I
> suspect that testing ext2 for directory performance is pointless.

Oh, I agree.  I just had a report of a regression in a certain distro,
which is frowned upon... :)  I'm positive ext4 nojournal would beat the
pants off it due to dir_index.

> My personal threshold for ext2 directories was 10k files before I
> considered it a lost cause, and all of your tests are with 10k+ files
> per directory.

Agreed, it's not very realistic but then it was a simple fix too.
Still took time though...

> Just another log on the fire beneath getting rid of ext2 (and
> eventually ext3) in favour of ext4, IMHO.  I'd be surprised if there
> are many benchmarks that ext2 can beat ext4 in nojournal mode, if
> allowed to enable "reversible" format changes like dir_index,
> uninit_bg, etc.

Hey, I wouldn't complain.

-Eric

> Cheers, Andreas
> 
> 
> 
> 
> 
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