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

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

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.

Like the FreeBSD one?

> 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.
> 

Did you think also about expanding the ring size to something bigger?

> 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
>                       
> Read 64K seq  BW MB/s Dom0 CPU        DomU CPU%
>       W       250             27.1           10.6
>       W/O     250             62.6           31.1
> 
> 
> The patch will be simple if we only use new methods. But we need consider 
> that user may use new kernel as backend while an older one as frontend. Also 
> need considerate live migration case. So the change become huge...

OK? I think you are implementing the extension documented in

changeset:   24875:a59c1dcfe968
user:        Justin T. Gibbs <justing@xxxxxxxxxxxxxxxx>
date:        Thu Feb 23 10:03:07 2012 +0000
summary:     blkif.h: Define and document the request number/size/segments 
extension

changeset:   24874:f9789db96c39
user:        Justin T. Gibbs <justing@xxxxxxxxxxxxxxxx>
date:        Thu Feb 23 10:02:30 2012 +0000
summary:     blkif.h: Document the Red Hat and Citrix blkif multi-page ring 
extensions

so that would be the max-requests-segments one?



> [RFC v1 1/5] 
>       In order to add new segment ring, refactoring the original code, split 
> some methods related with ring operation.
> [RFC v1 2/5]
>       Add the segment ring support in blkfront. Most of code is about 
> suspend/recover.
> [RFC v1 3/5]
>       As the same, need refractor the original code in blkback.
> [RFC v1 4/5]
>       In order to support different type of ring type in blkback, make the 
> pending_req list per disk.

Not sure why you structured the patches like this way, but it might
make sense to order them in 1, 3, 4, 2, 5 order. The 'pending_req'/per disk is 
an overall
improvement that fixes a lot of concurrent issues. I tried to implement this 
and ran
in an issue with grants still being active? Did you have issues with that or it 
worked just fine
for you?
> [RFC v1 5/5]
>       Add the segment ring support in blkback.

So .. where are the patches? Did I miss them?
> -ronghui
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel