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RE: [Xen-devel] vif interface dropping 80% packets

You are probably using jumbo packets for native, right? What is the MTU when you get 9.88 Gb/s? I was thinking MTU=1500  when I said unrealistic. Not sure why you cannot get higher MTU in Xen to work. I have not tried MTU > 1500 bytes in Xen myself  but I believe Herbert Xu has done that successfully.
If you get larger MTU to work, keep in mind that in Xen there is an extra data copy to transfer the packet from dom0 to guest which will have a higher impact on performance for larger MTUs when compared to linux. 

From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Reese Faucette
Sent: Tuesday, February 06, 2007 10:59 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] vif interface dropping 80% packets

Most likely your dom0 CPU is saturated.. It is unrealistic to expect full throughput of a 10 Gig NIC. I would be surprised if even linux could keep up with a receive rate of 10 Gb/s. Did you try the same experiment on native linux? In  my experiments, on a 4-way 2.8 Ghz Xeon, dom0 consumes ~75% of one cpu for processing receive packets while the guest consume ~55% of another CPU.
With native->native or even native->dom0, I get 9.88 Gb/s with 21% utilization of receive side CPU.  It's a nice machine and we make nice NICs ;-)  So, it's not unrealistic.
It is  expected that your dual CPU system saturates at a rate slighlty above 1 Ghz. (You are also consuming extra cycles to drop packets)
You could confirm that the CPU is saturating by running xentop while running your experiments.
You could avoid dropping packets and get a more realistic experiment by running a TCP experiment as Ian suggested
i have a pending note on that, TCP test is actually what I tried first, and the perf was terrible due to the same packet loss.  more info to come.
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