RE: [Xen-users] low network performance

Petersson, Mats
2007-05-31T16:48:06Z

You are already running para-virtualization, since you''re on an older
Ahtlon XP 1700+, these are a few years away from the current generation
that has the AMD-V feature to allow non-para-virtual OS''s to run on
Xen.


>
> Maybe the reason for the low network performance is
> somewhere else ?

Yes, I suspect the real problem here is "CPU congestion". Every packet
you send out goes from the DomU to Dom0, then from Dom0 to the othe DomU
(in the DomU -> DomU case). Since all three of these domains run on the
same processor, the overall latency is much higher than comparing
individual systems. Add to this the fact that the virtual system will
have a higher overhead simply because there is a hypervisor that want''s
to control things too [although this is probably only a small part of
the puzzle].

There is nothing you can really do about this, other than getting a new
system that has more CPU(-core)s to allow the processing of packets to
be done more in parallel.

> Could someone give me good options for the (tcp_rmem
> and so) variables in /et/sysctl.conf ? I found a howto
> therefore but changing the values didn''t had a
> reliable performance enhancement.

Probably not worth much, as you''ve found.
>
> A other reason could be that the domO is ''sucking'' in
> network traffic ... ?!
> Or that i run the system with 100MHz instead of 133MHz
> busfrequency ?! But i don''t think so cause i did that
> before too.

No, that will have a small effect in the whole scheme of things. Of
course, Xen and multiple guests will increase the memory bus-traffic, so
higher speed processors/memory controller will help to some extent, but
the 25% increase in bus-frequency will not give 25% performance
improvement here - probably more like 5-10% (or maybe none - depends on
how well the caching works in this case).

Do you want to have a guess why AMD and Intel are so interested in
virtualization? Nothing better for a processor manufacturer than
something that sucks up a bit more CPU power and makes customers buy new
processors, eh? ;-)

--
Mats
>
> For any hints, tips or links i will be very thankfully
> !
>
>
> Regards,
> funki
>
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>
>
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>
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