linux-kernel - Re: fio rand read/write regression with 2.6.32-rc3

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Date:	Sat, 10 Oct 2009 10:01:17 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: fio rand read/write regression with 2.6.32-rc3

On Sat, Oct 10 2009, Zhang, Yanmin wrote:
> Comparing with 2.6.23-rc1's result, fio rand read write has regression
> on my 2*4 core stoakley machine (8GB memory) with a JBOD of 12 disks.
> 
> Every disk has 8 1-GB files. Start 8 sub-processes per disk and every
> process random chooses a file on the disk to do 36 times of file read or
> write on the file and then choose another file.
> 
> 
> fio_mmap_rand_read_4k regresion is about 35%.

Heh, I seem to recollect I told Linus that this would cost is 30-40%
performance. So not totally crazy.

So yes, this isn't hugely unexpected. If you send me your fio job files,
I'll try and see what I can do about it.

> Bisect down to patch:
> 1d2235152dc745c6d94bedb550fea84cffdbf768 is first bad commit
> commit 1d2235152dc745c6d94bedb550fea84cffdbf768
> Author: Jens Axboe <jens.axboe@...cle.com>
> Date:   Fri Oct 2 19:27:04 2009 +0200
> 
>     cfq-iosched: add a knob for desktop interactiveness
> 
> 
> After I revert the patch against 2.6.23-rc3, fio_mmap_rand_read_4k regression
> disappears.
> 
> fio_mmap_randrw_4k has less than 20% regression and reverting the patch
> could restore performance.
> 
> On another stoakley machine with another JBOD, we see the similiar regression.
> 
> ffsb rand read/write has a bigger regression and reverting the patch
> could restore performance.
> 
> Yanmin
> 
> 

-- 
Jens Axboe

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