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Re: [Xen-devel] IO speed limited by size of IO request (for RBD driver)

On 27/04/2013 12:06 AM, Roger Pau Monné wrote:
On 23/04/13 21:05, Steven Haigh wrote:
Sorry - resending this to Felipe as well - as I started talking to him
directly previously.

Felipe, to bring you up to date, I've copied over the blkback files from
Rogers indirect kernel over the vanilla 3.8.8 kernel files, built and
tested. Results below:

Bringing this into context in a nutshell - results showed about 5MB/sec improvement when using buffered disk access - totalling ~57MB/sec write speed vs ~98MB/sec when using the oflag=direct flag to dd.

When talking about back porting a few indirect patches to mainline blkback (3.8.8 atm):
On 24/04/2013 4:13 AM, Roger Pau Monné wrote:
I think it requires a non-trivial amount of work, what you could do as a
test is directly replace the affected files with the ones in my tree, it
is not optimal, but I don't think it's going to cause problems, and you
could at least see if indirect descriptors solve your problem.

Ok, I copied across those files, built, packaged and installed them on
my Dom0. Good news is that its a little quicker, bad news is not by much.

Could you try increasing xen_blkif_max_segments variable in
xen-blkfront.c to 64 or 128? It is set to 32 by default. You will only
need to recompile the DomU kernel after this, the Dom0 is able to
support up to 256 indirect segments.

I'll have to look at this. All DomU's are Scientific Linux 6.4 systems - so essentially RHEL6.4 and so on. I haven't built a RH kernel as yet - so I'll have to look at what is involved. It might be as simple as rebuilding a normal SRPM.

Also, I think we should bring this conversation back to xen-devel.


Steven Haigh

Email: netwiz@xxxxxxxxx
Web: https://www.crc.id.au
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