| |
|
 |
|
 |
|
|
|
| |
|
|
xen-devel
Re: [Xen-devel] Slow guest network I/O when CPU is pegged - Looking for
On 7 Apr 2006, at 19:25, Matt Ayres wrote:
Ok, so we all know that guest network I/O is slow when the system
CPU's are being utilized extensively whether it be from dom0 or from
other guests. Lots of people have written about this and I can post
concrete tests if required.
I'm just looking for one of the Xen developers to acknowledge that
they have been able to replicate the problem and it is indeed being
worked on or will be sometime in the near future. No one has
acknowledged any of the previous threads on either list so I want to
make sure it is an outstanding issue that is not being overlooked.
It depends on the setup but poor scheduling is the main reason for poor
network performance, usually. SEDF seems to have some problems with
real-time domains (like domain0 with its default scheduling parameters)
and gives them all the CPU they want -- this is obviously going to be
bad if a client domain is scheduled on the same CPU. Since UDP has no
flow control, dom0 can keep itself busy generating or forwarding UDP
packets to the domU that get dropped continually in netback driver.
DomU will hardly ever get scheduled. Even in the case of TCP, any drops
will be interpreted as congestion and transmit rate will be cut.
Basically I think the SEDF scheduler needs cleaning up: probably by
removing the mass of confusing conditionally compiled options and then
focusing on the remaining code that is actually compiled in. Another
option is to try specifying the BVT scheduler and see if that works
better. Or try setting dom0 to have non-real-time guarantees. Or give
dom0 its own hyperthread on an Intel system (strongly recommended if
it's possible).
Apart from that, if you really are genuinely loading up CPUs with
CPU-intensive workloads, and expecting them also to be able to process
a significant amount of network traffic then something has to give. You
can only run CPUs at 100%.
-- Keir
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
| |
|
Home