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xen-devel
Re: [Xen-devel] [RFC][PATCH] scheduler: credit scheduler for client virt
Thanks for your information.
George Dunlap wrote:
There was a paper earlier this year about scheduling and I/O performance:
http://www.cs.rice.edu/CS/Architecture/docs/ongaro-vee08.pdf
One of the things he noted was that if a driver domain is accepting
network packets for multiple VMs, we sometimes get the following
pattern:
* driver domain wakes up, starts processing packets. Because it's in
"over", it doesn't get boosted.
* Passes a packet to VM 1, waking it up. It runs in "boost",
preempting the (now lower-priority) driver domain.
* Other packets (possibly even for VM 1) sit in the driver domain's
queue, waiting for it to get cpu time.
I don't read the paper yet, but I think our approach is effective in
this problem.
However, if driver domain consumes cpu time too much, we couldn't
prevent it from becoming "over" priority. Otherwise, we could keep it
with "under" or "boost" priority.
Their tests, for 3 networking guests and 3 cpu-intensive guests,
showed a 40% degradation in performance due to this problem. While
we're thinking about the scheduler, it might be worth seeing if we can
solve this.
Firstly, I'd like to read the paper.
Regards,
Naoki Nishiguchi
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