RE: [Xen-devel] [PATCH] xen, tools/python/xen: pincpu support vcpus, add vcpu to cpu map

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > "xm pincpu mydom 1 2,4-6" which would allow VCPU 1 of mydom 
> to run on 
> > CPUs 2,4 and 5 but no others. -1 would still mean "run anywhere". 
> > Having this functionality is really important before we can 
> implement 
> > any kind of CPU load ballancer.
> 
> Interesting idea.  I don't see anything in the schedulers 
> that would take advantage of that sort of definition.  AFAIK, 
> exec_domains are never migrated unless told to do so via 
> pincpu.  Does the new scheduler do this?  Or is this more of 
> setting up the rules that the load balancer would query to 
> find out where it can migrate vcpus?

I see having this as a pre-requisite for any fancy new scheduler (or as
a first step, CPU load ballancer). Without it, I think it'll be
scheduling anarchy :-)

> > Secondly, I think it would be really good if we could have some 
> > hierarchy in CPU names. Imagine a 4 socket system with dual 
> core hyper 
> > threaded CPUs. It would be nice to be able to specify the 
> 3rd socket, 
> > 1st core, 2nd hyperthread as CPU "2.0.1".
> > 
> > Where we're on a system without one of the levels of hierarchy, we 
> > just miss it off. E.g. a current SMP Xeon box would be "x.y". This 
> > would be much less confusing than the current scalar representation.
> 
> I like the idea of being able to specify "where" the vcpu 
> runs more explicitly than 'cpu 0', which does not give any 
> indication of physical cpu characteristics.  We would 
> probably need to still provide a simple mapping, but allow 
> the pincpu interface to support a more specific target as 
> well as the more generic.
> 
> 2-way hyperthreaded box:
> CPU     SOCKET.CORE.THREAD
> 0       0.0.0
> 1       0.0.1
> 2       1.0.0
> 3       1.0.1
> 
> That look sane?

Yep, that's what I'm thinking. I think its probably worth squeezing out
unsused levels of hierarchy, e.g. just having SOCKET.THREAD in the above
example. Keeping it pretty generic makes sense too. E.g. imagine a big
ccNUMA system with a 'node' level above that of the actual CPU socket.

Best,
Ian

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