Re: [Xen-devel] Xen & I/O in clusters - problems! New Information

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> Between two Xen dom0 domains (between two physical computers in the 
> cluster) we got these strange results:
> (We use ttcp socketbuffsize, 10^4 -> 10^6)
> 
> Kernel 2.6:
> Xen Dom0 -> Xen Dom0: ca. 80 000 KB/s (?)
> 
> Native Linux:
> Native Linux -> Native Linux: ca. 114 000 KB/s
> 
> What is new and strage is that Xen Dom0 use about 60% of the CPU when 
> transfering or receiving, while
> Native Linux ony use 6-7%(!) It seems like we have a problem with the 
> DMA here(?). We use Xen 2.0,
> Gigabit ethernet.

dom0 to dom0 performance really shouldn't be any difference from
native. It certainly isn't on any of our machines.

The only thing I can think of is that something stupid might be
happening with interrupts on your machines. Can you compare the
rate that the relevant interrupts are going up in
/proc/interrupts between xenLinux and native.

There's no interrupt sharing or anything daft like that going on?
Are you using NAPI on the native e1000 linux driver?


Ian


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