[Xen-devel] Is CPU overhead really independent of packet size in Xen?

["Liang Yang" <multisyncfe991@xxxxxxxxxxx>]

Hi,
I'm reading some Xen performance slides which is published on XenSummit 
(www.xensource.com/files/summit_3/perf-isolation-gupta.pdf). The presenter 
claims the CPU overhead is independent of network packet size in Xen VM 
domains. I haven't done much research on network I/O on Xen, but I have done 
many experiments on disk I/O.
Based on my disk I/O experimental results, I found out, generally the CPU 
utilization decrease as the I/O packet size increase which is consistent 
with the IPv4 forwarding experiments I did before (not on Xen, on plain IA32 
Linux). The only exception I noticed is DomainUF. For both small size and 
large size sequential I/O, the CPU utilization in DomainUF remains almost 
constant (100%) while CPU utilization drops for 4k and 8K random I/O.
If anyone in this mailing list has done similar experiments, please adivse 
the difference when considering CPU utilization for network I/O and disk 
I/O? or should both network I/O and disk I/O have the same curve of CPU 
utilization vs. Packet Size?
Thanks,

Liang


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