On Mon, Feb 17, 2020 at 09:23:52PM +0800, 王贇 wrote:

FYI, by monitoring locality, we found that the kvm vcpu thread is not
covered by NUMA Balancing, whatever how many maximum period passed, the
counters are not increasing, or very slowly, although inside guest we are
copying memory.

Later we found such task rarely exit to user space to trigger task
work callbacks, and NUMA Balancing scan depends on that, which help us
realize the importance to enable NUMA Balancing inside guest, with the
correct NUMA topo, a big performance risk I'll say :-P

That's a bug in KVM, see:

  https://lkml.kernel.org/r/20190801143657.785902257@linutronix.de
  https://lkml.kernel.org/r/20190801143657.887648487@linutronix.de

ISTR there being newer versions of that patch-set, but I can't seem to
find them in a hurry.