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

[Zhang, Yanmin]

On Sat, 2009-10-10 at 10:02 +0200, Jens Axboe wrote:
> 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?
Echo 0 to low_latency makes the regression become less than 3%.


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