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Re: [libvirt] [PATCH RFC v2] qemu: Support numad

Note numad will attempt to manage / balance processes after they're launched, but the ideal case is libvirt pre-places them in a good spot and they never move....

On 03/07/2012 10:38 AM, Osier Yang wrote:
On 2012年03月07日 21:48, Daniel P. Berrange wrote:
On Wed, Mar 07, 2012 at 09:55:16PM +0800, Osier Yang wrote:
numad is an user-level daemon that monitors NUMA topology and
processes resource consumption to facilitate good NUMA resource
alignment of applications/virtual machines to improve performance
and minimize cost of remote memory latencies. It provides a
pre-placement advisory interface, so significant processes can
be pre-bound to nodes with sufficient available resources.

More details: http://fedoraproject.org/wiki/Features/numad

"numad -w ncpus:memory_amount" is the advisory interface numad
provides currently.

This patch add the support by introducing a bool XML element:

If it's specified, the number of vcpus and the current memory
amount specified in domain XML will be used for numad command
line (numad uses MB for memory amount):
numad -w $num_of_vcpus:$current_memory_amount / 1024

The advisory nodeset returned from numad will be used to set
domain process CPU affinity then. (e.g. qemuProcessInitCpuAffinity).

If the user specifies both CPU affinity policy (e.g.
(<vcpu cpuset="1-10,^7,^8">4</vcpu>) and XML indicating to use
numad for the advisory nodeset, the specified CPU affinity will be

I'm not sure that's a good idea. When we do dynamic generation
of parts of libvirt XML, we tend to report in the XML what was
generated, and if 2 parts contradict each other we shouldn't
silently ignore it.

Agreed, v1 overrides the cpuset="1-10,^6", but I thought it
could be confused for user to see things are different after
domain is started.

eg, with VNC with autoport=yes we then report the generated
port number.

Similarly with<cpu> mode=host, we then report what the host
CPU features were.

So, if we want to auto-set placement for a guest we should
likely do this via the<vcpu> element

eg, Current mode where placement is completely static

- Input XML:

<vcpu placement="static" cpuset="1-10" />

- Output XML:

<vcpu placement="static" cpuset="1-10" />

Or where we want to use numad:

- Input XML:

<vcpu placement="auto"/>

- Output XML:

<vcpu placement="auto" cpuset="1-10" />

I must admit this is much better. :-)

The current numad functionality you propose only sets the initial guest
placement. Are we likely to have a mode in the future where numad will
be called to update the placement periodically for existing guests ?

Very possiable, now numad just provides the advisory interface,
in future I guess it could manage the placement dynamically.

If so, then "placement" would need to have more enum values.

I will post a v3 tomorrow.


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