On 8/31/2010 6:00 PM, matthew.r.rohrer@xxxxxxxxxx wrote:
I have been getting degrading network performance with newer versions of KVM and was wondering if this was expected? It seems like a bug, but I am new to this and maybe I am doing something wrong so I thought I would ask. KVM Host OS: Fedora 12 x86_64 KVM Guest OS Tiny Core Linux 2.6.33.3 kernel I have tried multiple host kernels 2.6.31.5, 2.6.31.6, 2.6.32.19 and 2.6.35.4 along with versions qemu-kvm 11.0 and qemu-system-x86_64 12.5 compiled from from qemu-kvm repo.
I can't say anything about the kernel version making things worse. At least for the qemu-kvm version, you should be using -device and -netdev instead of -net nic -net tap (see *http://git.qemu.org/qemu.git/tree/docs/qdev-device-use.txt since it's not in the 0.12 tree).*
Setup is: 2 hosts with 1 guest on each connected by 10 Gb nic. I am using virtio and have checked that hardware acceleration is working. Processor usage is less than 50% on host and guests. Here is what I am seeing, I will just include guest to guest statistics, I do have more (host to guest, etc.) if interested:
<snip results>
My goal is to get as much bandwidth as I can between the 2 guests running on separate hosts. The most I have been able to get is ~4 Gb/s running 4 threads on iperf from guest A to guest B. I cannot seem to get much over 1.5Gb/s from guest to guest with a single iperf thread. Is there some sort of know send limit per thread? Is it expected that the latest version of the kernel and modules perform worse than earlier versions in the area of network performance ( I am guessing not, am I doing something wrong?)? I am using virtio and have checked that hardware acceleration is working. 4 iperf threads host to host yields ~9.5 Gb/s. Any ideas on how I can get better performance with newer versions? I have tried using vhost in 2.6.35 but I get the vhost could not be initialized error. The only thing I could find on the vhost error is that selinux should be off which it is. I am looking for ideas on increasing the bandwidth between guests and thoughts on the degrading performance.
Vhost-net is probably your best bet for maximizing throughput. You might try a separate post just for the vhost error if nobody chimes in about it here.
Thanks for your help! --Matt
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