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

["Duan, Ronghui" <ronghui.duan@xxxxxxxxx>]

> form xentop.
> > Read 1K random      IOPS       Dom0 CPU     DomU CPU%
> >             W       52005.9 86.6    71
> >             W/O     52123.1 85.8    66.9
> 
> So I am getting some different numbers. I tried a simple 4K read:
> 
> [/dev/xvda1]
> bssplit=4K
> rw=read
> direct=1
> size=4g
> ioengine=libaio
> iodepth=64
> 
> 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
> 
What type of backend file you are using? In order to remove the influence of 
cache in Dom0, I use a physical partition as backend.
In code level, although there is some overhead in my patch compared to 
original, but it should not to be so big. :)

-ronghui

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> Sent: Saturday, September 08, 2012 1:49 AM
> To: Duan, Ronghui
> Cc: xen-devel@xxxxxxxxxxxxx; Ian.Jackson@xxxxxxxxxxxxx;
> Stefano.Stabellini@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [RFC v1 0/5] VBD: enlarge max segment per request in
> blkfront
> 
> On Thu, Aug 16, 2012 at 10:22:56AM +0000, Duan, Ronghui wrote:
> > Hi, list.
> > The max segments for request in VBD queue is 11, while for Linux OS/ other
> VMM, the parameter is set to 128 in default. This may be caused by the limited
> size of ring between Front/Back. So I guess whether we can put segment data
> into another ring and dynamic use them for the single request's need. Here is
> prototype which don't do much test, but it can work on Linux 64 bits 3.4.6
> kernel. I can see the CPU% can be reduced to 1/3 compared to original in
> sequential test. But it bring some overhead which will make random IO's cpu
> utilization increase a little.
> >
> > Here is a short version data use only 1K random read and 64K sequential read
> in direct mode. Testing a physical SSD disk as blkback in backend. CPU% is got
> form xentop.
> > Read 1K random      IOPS       Dom0 CPU     DomU CPU%
> >             W       52005.9 86.6    71
> >             W/O     52123.1 85.8    66.9
> 
> So I am getting some different numbers. I tried a simple 4K read:
> 
> [/dev/xvda1]
> bssplit=4K
> rw=read
> direct=1
> size=4g
> ioengine=libaio
> iodepth=64
> 
> 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
> 
> 
> >
> > Read 64K seq        BW MB/s Dom0 CPU        DomU CPU%
> >     W       250             27.1           10.6
> >     W/O     250             62.6           31.1
> 
> Hadn't tried that yet.

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