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Re: [Xen-devel] Disk IO scheduling in XEN
On 3/24/2011 1:19 PM, Paresh Nakhe wrote:
Hi,
We are working on a project to modify the disk scheduling
mechanism in XEN a bit in an attempt to improve it. In the paper
"Xen and the Art of Virtualization" following is mentioned.
"Xen services batches of requests from competing domains in a
simple round-robin fashion; these are then passed to a standard
elevator
scheduler before reaching the disk hardware"
We were going through linux-jeremy source code in an attempt to
map the above in code. We could not however do so. On the contrary
we came to the conclusion that there is no such mechanism. Domain
0 services requests as soon as it receives a hypercall from a
guest domain. Are we right?
Ian Campbell forward-ported the 2.6.18-xen.hg patches for this but I
don't think that they've been merged into the main git 2.6.32 stable
tree yet. Check the list archives for the subject line "unfair
servicing of DomU vbd requests" for more information on this.
Which one would be better first come first serve or round robin
and why?
Of the two, RR, because domains can become starved otherwise.
-John
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