Re: [Xen-users] GPLPV xennet bsod when vcpu>15

[Dion Kant <dion@xxxxxxxxxx>]

On 06/25/2012 02:07 AM, James Harper wrote:
>>> Is this a known problem?
>>>
>> Not until you just mentioned it. I've never tried it, but looking at the 
>> code I'd
>> expect that the limit would have been 32 or 64, not 16. I can't think why
>> xennet would be caring about the number of processors either, although
>> that could just be a symptom of a problem in xenpci.
>>
>> I'll try and find some time to test it myself.
>>
> I think I can see the problem... I'm making the assumption that the processor 
> numbering is linear such that in a system with NdisSystemProcessorCount() 
> CPU's, they are numbered from 0 to NdisSystemProcessorCount()-1, but I bet 
> that with >16 processors they aren't numbered linearly (eg 0-15 + 32-47 or 
> something).
>
> How quickly do you need a fix?
>
> James
>
 I am not in a hurry with this. However, I recently ran into a
performance related problem regarding domU<-->domU communication.
Searching the list, I found that this is also related to multiple cores
(I experienced before that going to "extremes" in software space
revealed errors nobody else noticed before).

I have the following issue (further referred to as the multicore xennet
issue) on hardware with 16 cores available.

1. With a configuration with two W2K8 servers running multiple cores
each, domU<-->domU communication is limited to around 6/7 MB/s.
2. Configuring the two domUs with each one cpu, the domU<-->domU
communication goes up to about 80 to 100 MB/s. Probably this is limited
by the disk I/O.

However, on the "big dom0 machine" with 64 cores available and >500GB
RAM, I had not noticed this issue so far. However there the
configuration is one domU with 15 cores using xennet and the other domU
with 48 cores, running GPLPV as well except for the network interface
which is configured with Qemu's e1000.

I can spend time on more testing on this multicore xennet issue and
publish the results here if this is interesting for the list.

1. First I am going to capture the details of the first mentioned BSOD;
2. I'll repeat the 2 times GPLPV-ed domU multi core configuration and
repeat the measurements.

Thanks so far,

Dion


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