RE: [Xen-devel] vCPU pinning

["Kaushik Barde" <Kaushik_Barde@xxxxxxxxxxx>]

Thanks, Mark.

Sorry about asking a very specific question without giving its context.
Your response is appreciated.
We would like to use it to enforce better CPU power management, first
goal is to implement "reliable" enough CPU frequency scaling and create
_CST mapping to a governor running in Xen context, which can map into
existing user mode frequency scalars.

-Kaushik


-----Original Message-----
From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On Behalf Of Mark
Williamson
Sent: Monday, October 08, 2007 9:36 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Kaushik Barde
Subject: Re: [Xen-devel] vCPU pinning

> I would like to "pin" vcpu to a domain,
> Can someone please point to me if there's such a support?

Your question didn't quite make sense, but I think I see what you mean -
it's 
just that the terminology is a bit complicated!

If you consider a domain as being "like a process" then VCPUs are 
like "threads".  They're the parts of the domain that get scheduled on
the 
real CPUs and do work.  *within* the domain, these will be shared out
between 
processes the OS is running but /Xen doesn't really know about this/.
It 
just sees a bunch of VCPUs from a domain that it can run, and a bunch of
real 
logical CPUs that it can run them on.

You can pin a VCPU to a real logical CPU (that's a core or a hyperthread
on 
the host machine).  This can be used to divide up the machine more
strictly, 
enforce separation or quality of service, etc.

You can specify pinning at runtime using the command "xm vcpu-pin", or
in the 
domain config file using the "CPUs" variable.  I believe it's possible
to set 
a mask of "possible CPUs" for all VCPUs or for individual VCPUs.

Hope this helps you.

Cheers,
Mark

PS. "how do I...?" questions are generally better directed to the
xen-users 
mailing list - they're liable to get more responses and discussion there
due 
to the higher subscriber cound and user focus.

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no
pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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