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

  • To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Reese Faucette" <reese@xxxxxxxx>
  • Date: Tue, 6 Feb 2007 10:58:37 -0800
  • Delivery-date: Tue, 06 Feb 2007 10:58:19 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

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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