Re: [PATCH v3 4/7] util: Add write-only "node-affinity" property for ThreadContext

[Markus Armbruster <armbru@redhat.com>]

David Hildenbrand <david@redhat.com> writes:

> Let's make it easier to pin threads created via a ThreadContext to
> all host CPUs currently belonging to a given set of host NUMA nodes --
> which is the common case.
>
> "node-affinity" is simply a shortcut for setting "cpu-affinity" manually
> to the list of host CPUs belonging to the set of host nodes. This property
> can only be written.
>
> A simple QEMU example to set the CPU affinity to host node 1 on a system
> with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to
> host node 1:
>     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
>     ]
>
> We cannot query the node-affinity:
>     (qemu) qom-get tc1 node-affinity
>     Error: Insufficient permission to perform this operation
>
> 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. We'll wire
> this up next to make it work.
>
> Note that if the host CPUs for a host node change due do CPU hot(un)plug
> CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext
> was started, the CPU affinity will not get updated.
>
> Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
> Acked-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: David Hildenbrand <david@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 8013ba4b82..5a2db663f0 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -839,10 +839,17 @@
>  #                threads created in the thread context (default: QEMU main
>  #                thread CPU affinity)
>  #
> +# @node-affinity: the list of host node numbers that will be resolved to a list
> +#                 of host CPU numbers used as CPU affinity. This is a shortcut
> +#                 for specifying the list of host CPU numbers belonging to the
> +#                 host nodes manually by setting @cpu-affinity. (default: QEMU
> +#                 main thread affinity)

Would you mind breaking these lines a bit earlier, like you did for the
previous member?

> +#
>  # Since: 7.2
>  ##
>  { 'struct': 'ThreadContextProperties',
> -  'data': { '*cpu-affinity': ['uint16'] } }
> +  'data': { '*cpu-affinity': ['uint16'],
> +            '*node-affinity': ['uint16'] } }
>  
>  
>  ##

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