Re: [Xen-users] xennet windows pv performance

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, Mar 02, 2008 at 05:01:28PM +1100, James Harper wrote:
> I've just pushed some changes to hg that seem to speed things up a bit
> for me.
> 
> On one machine with 2 x dual core 2.4Ghz AMD cpu's, testing with iperf
> from DomU to Dom0 I get:
> Windows (vcpus = 2) - ~500MBits/sec - ~66% cpu utilization (eg 100% on
> one, and 33% on the second cpu)
> Linux (vcpus = 1) - ~2200MBits/sec
> 

Was this Linux domU HVM (using PV drivers) or PV? 

In this box you have 4 physical cpus.. windows vm has 2 vcpus so your dom0 has 2
pcpus dedicated only for it.. 

> On another machine with 1 x dual core 1.8Ghz AMD cpu, testing as above I
> get:
> Windows (vcpus = 2) - ~65MBits/sec - ~100% cpu utilization (eg 100% on
> both cpu's)
> Linux - can't test as I don't have any Linux DomU's set up presently.
> 
> I don't think there is enough difference in raw CPU power to account for
> the 7x performance difference between the two physical machines... it
> must be something else.
> 

Hmm.. do these CPU's have different sizes of caches? Then again it can't
cause that big difference.. 

Could it be some xen scheduling issue? You're using 2 vcpus for windows, and
in this second box you only have 2 pcpus.. and they're both 100% used so no
dedicated pcpus for dom0.. 

> Anyway, on the second machine my performance is up from about
> 40MBits/sec so I think I'm making progress.
> 

Nice!

-- Pasi

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