Re: [Xen-devel] [RFC v1 0/5] VBD: enlarge max segment per request in blkfront

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Sep 17, 2012 at 06:33:29AM +0000, Duan, Ronghui wrote:
> At last, I saw the regression in random io.
> This is a patch to fix the performance regression. Original the pending 
> request members are allocated from the stack, I alloc them when each request 
> arrives in my last patch. But it will hurt performance. In this fix, I alloc 
> all of them when blkback init. But due to some bugs there, we can't free it, 
> the same to other pending requests member. I am looking for the reason. But 
> have no idea for this now. 
> Konrad, thanks for your comments. Could you have a try when you have time.

Sure.  I get now:

  read : io=4096.0MB, bw=144258KB/s, iops=36064 , runt= 29075msec

so much better I/O.

> > > > > >> And with your patch got:
> > > > > >>   read : io=4096.0MB, bw=92606KB/s, iops=23151 , runt=
> > > > > >> 45292msec
> > > > > >>
> > > > > >> without:
> > > > > >>   read : io=4096.0MB, bw=145187KB/s, iops=36296 , runt=
> > > > > >> 28889msec

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