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

[Jens Axboe]

On Sat, Oct 10 2009, 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.

Oh, and can you check whether setting

/sys/block/sdX/queue/iosched/low_latency

to 0 for the involved devices makes the regression go away?

-- 
Jens Axboe

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