David Hildenbrand <da...@redhat.com> writes:
> Let's make it easier to pin threads created via a ThreadContext to
> all CPUs currently belonging to a given set of NUMA nodes -- which is the
> common case.
>
> "node-affinity" is simply a shortcut for setting "cpu-affinity" manually
> to the list of CPUs belonging to the set of nodes. This property can only
> be written.
>
> A simple QEMU example to set the CPU affinity to Node 1 on a system with
> two NUMA nodes, 24 CPUs each:
> qemu-system-x86_64 -S \
> -object thread-context,id=tc1,node-affinity=1
>
> And we can query the cpu-affinity via HMP/QMP:
> (qemu) qom-get tc1 cpu-affinity
> [
> 1,
> 3,
> 5,
> 7,
> 9,
> 11,
> 13,
> 15,
> 17,
> 19,
> 21,
> 23,
> 25,
> 27,
> 29,
> 31,
> 33,
> 35,
> 37,
> 39,
> 41,
> 43,
> 45,
> 47
> ]
Double-checking my understanding: on this system, the even CPUs belong
to NUMA node 0, and the odd ones to node 1. Setting node-affinity=1 is
therefore sugar for setting cpu-affinity to the set of even CPUs.
Correct?
> We cannot query the node-affinity:
> (qemu) qom-get tc1 node-affinity
> Error: Insufficient permission to perform this operation
The error message is somewhat misleading. "Insufficient permission"
suggests this could work if I had more "permission". Not the case. The
message comes from object_property_get(), i.e. it's not this patch's
fault. I'll post a patch to improve it.
> But note that due to dynamic library loading this example will not work
> before we actually make use of thread_context_create_thread() in QEMU
> code, because the type will otherwise not get registered.
>
> Note that if the CPUs for a node change due do physical CPU hotplug or
> hotunplug (e.g., lscpu output changes) after the ThreadContext was started,
> the CPU affinity will not get updated.
>
> Reviewed-by: Michal Privoznik <mpriv...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> qapi/qom.json | 9 ++++-
> util/meson.build | 2 +-
> util/thread-context.c | 84 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 93 insertions(+), 2 deletions(-)
>
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 67d47f4051..cb6f700c0c 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -839,10 +839,17 @@
> # created in the thread context (default: QEMU main thread
> # affinity)
> #
> +# @node-affinity: the list of node numbers that will be resolved to a list
> +# of CPU numbers used as CPU affinity. This is a shortcut for
> +# specifying the list of CPU numbers belonging to the nodes
> +# manually by setting @cpu-affinity. (default: QEMU main
> thread
> +# affinity)
> +#
> # Since: 7.2
> ##
> { 'struct': 'ThreadContextProperties',
> - 'data': { '*cpu-affinity': ['uint16'] } }
> + 'data': { '*cpu-affinity': ['uint16'],
> + '*node-affinity': ['uint16'] } }
>
>
> ##
[...]
