Re: [PATCH] util: NUMA aware memory preallocation

[Paolo Bonzini]

On 5/11/22 12:10, Daniel P. Berrangé wrote:
> If all we needs is NUMA affinity, not CPU affinity, then it would
> be sufficient to create 1 I/O thread per host NUMA node that the
> VM needs to use. The job running in the I/O can spawn further
> threads and inherit the NUMA affinity.  This might be more clever
> than it is needed though.
>
> I expect creating/deleting I/O threads is cheap in comparison to
> the work done for preallocation. If libvirt is using -preconfig
> and object-add to create the memory backend, then we could have
> option of creating the I/O threads dynamically in -preconfig mode,
> create the memory backend, and then delete the I/O threads again.

I think this is very overengineered.  Michal's patch is doing the 
obvious thing and if it doesn't work that's because Libvirt is trying to 
micromanage QEMU.

As mentioned on IRC, if the reason is to prevent moving around threads 
in realtime (SCHED_FIFO, SCHED_RR) classes, that should be fixed at the 
kernel level.

Paolo