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

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Date:	Sat, 10 Oct 2009 17:52:13 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Jens Axboe <jens.axboe@...cle.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, 2009-10-10 at 10:01 +0200, Jens Axboe wrote:
> 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.
See the attachment.

> 
> > 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
> > 
> > 
> 

Download attachment "job_file_st01_fio_mmap_randread_4k.gz" of type "application/x-gzip" (1125 bytes)