On Tue, 25 Sep 2018 14:37:15 +0200 Jiri Denemark <jdenemar@redhat.com> wrote:
On Tue, Sep 25, 2018 at 12:02:40 +0200, Wim Ten Have wrote:
From: Wim ten Have <wim.ten.have@oracle.com>
This patch extends the guest domain administration adding support to automatically advertise the host NUMA node capabilities obtained architecture under a guest by creating a vNUMA copy.
I'm pretty sure someone would find this useful and such configuration is perfectly valid in libvirt. But I don't think there is a compelling reason to add some magic into the domain XML which would automatically expand to such configuration. It's basically a NUMA placement policy and libvirt generally tries to avoid including any kind of policies and rather just provide all the mechanisms and knobs which can be used by applications to implement any policy they like.
The mechanism is enabled by setting the check='numa' attribute under the CPU 'host-passthrough' topology: <cpu mode='host-passthrough' check='numa' .../>
Anyway, this is definitely not the right place for such option. The 'check' attribute is described as
"Since 3.2.0, an optional check attribute can be used to request a specific way of checking whether the virtual CPU matches the specification."
and the new 'numa' value does not fit in there in any way.
Moreover the code does the automatic NUMA placement at the moment libvirt parses the domain XML, which is not the right place since it would break migration, snapshots, and save/restore features.
Howdy, thanks for your fast response. I was Out Of Office for a while unable to reply earlier. The beef of this code does indeed not belong under the domain code and should rather move into the NUMA specific code where check='numa' is simply badly chosen. Also whilst OOO it occurred to me that besides auto partitioning the host into a vNUMA replica there's probably even other configuration target we may introduce reserving a single NUMA-node out of the nodes reserved for a guest to configure. So my plan is to come back asap with reworked code.
We have existing placement attributes for vcpu and numatune/memory elements which would have been much better place for implementing such feature. And event cpu/numa element could have been enhanced to support similar configuration.
Going over libvirt documentation I am more appealed with vcpu area. As said let me rework and return with better approach/RFC asap. Rgds, - Wim10H.
Jirka
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