Re: [PATCH 1/2] ext2: speed up file creates by optimizing rec_len functions

[Eric Sandeen <sandeen@redhat.com>]

On 12/7/10 3:07 PM, Andrew Morton wrote:
> On Tue, 07 Dec 2010 11:51:05 -0600
> Eric Sandeen <sandeen@redhat.com> wrote:
> 
>> The addition of 64k block capability in the rec_len_from_disk
>> and rec_len_to_disk functions added a bit of math overhead which
>> slows down file create workloads needlessly when the architecture
>> cannot even support 64k blocks, thanks to page size limits.
>>
>> The directory entry checking can also be optimized a bit
>> by sprinkling in some unlikely() conditions to move the
>> error handling out of line.
>>
>> bonnie++ sequential file creates on a 512MB ramdisk speeds up
>> from about 2200/s to about 2500/s, about a 14% improvement.
>>
> 
> hrm, that's an improbably-large sounding improvement from eliminating
> just a few test-n-branches from a pretty heavyweight operation.

And yet ...

Yeah, I dunno.  Part of it is that ext2_add_link does a linear
search, so when you do rec_len_from_disk 50,000 times on a dir,
that little bit adds up quite badly I suppose.

Retesting at a bunch of different number-of-files in bonnie
(with a small sample size so probably a little noise)

	|files per sec|
files	stock	patched	delta
10,000	12300	14700	+19%
20,000	 6300	 7600	+20%
30,000	 4200	 5000	+20%
40,000	 3150	 3700	+17%
50,000	 2500	 3000	+20%

(again all on a 512MB ramdisk)

*shrug* I'll believe my lyin' eyes, I guess. :)

-Eric