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Re: [Xen-users] maximum domU performance

To: Jeff Sturm <jeff.sturm@xxxxxxxxxx>
Subject: Re: [Xen-users] maximum domU performance
From: Bruce Edge <bruce.edge@xxxxxxxxx>
Date: Thu, 15 Oct 2009 09:03:57 -0700
Cc: "Fajar A. Nugraha" <fajar@xxxxxxxxx>, Zu <zuzhihui@xxxxxxxxx>, Xen User-List <Xen-users@xxxxxxxxxxxxxxxxxxx>
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On Thu, Oct 15, 2009 at 7:40 AM, Jeff Sturm <jeff.sturm@xxxxxxxxxx> wrote:
>> -----Original Message-----
>> What if the dom0 has no tasks once the domU is up and running?
>> eg: disable syslog, cron, etc on dom0
>> Can one assign all cores to the domU?
>> Or, must one core remain idle dedicated to handling dom0 processing?
> Dom0 can share a core, but it'll be timesliced if the dom0 has things to
> do.  Which may not be good overall.  I like to pin dom0 to one (or more)
> core, and leave everything else to domU.
> Whether this helps you or not depends on what the domU is doing.  If
> your domU is compute-intensive, it may benefit from having access to all
> cores.  But if it routinely does any block or network I/O, the dom0
> needs to get involved, since that's where the backend drivers usually
> run.  And if dom0 has to wait for a CPU to  become available, that may
> delay domU I/O.
> -Jeff

This clarifies a lot, thanks Jeff.
I'm not intentionally being thick, but I want to cover all possibilities :-)
To extrapolate from that, if I wanted to avoid having dom0 competing
for a core, I would have to pass through any devices the domU needed
to access, or have hardware that supports sr-iov?

Just for the sake of argument, if I could eliminate all hardware
proxying requirements of the dom0, would a domU be able to hold on to
all the cores, or would the dom0 or  hypervisor still periodically
"steal" a core?


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