[vfio-users] cpu usage in guest != cpu usage in host, even with exclusive pinning

[Alex Williamson]

If this is the issue I think it is, the unraid folks bisected this and
found the culprit as:

aca6ff2 KVM: dynamic halt-polling

(
https://github.com/torvalds/linux/commit/aca6ff29c4063a8d467cdee241e6b3bf7dc4a171
)

It seems to be a poor interaction of the halt polling interval vs the timer
ticks on win10.  You can pick a different polling interval with the kvm
module option halt_poll_ns.  The default is 500000.  It seemed that setting
this to 400000 or lower resolves the issue.  You can do this via a modprobe
entry, 'options kvm halt_poll_ns=400000' or on the kernel command line with
kvm.halt_poll_ns=400000.  You can also change it dynamically via 'echo
400000 > /sys/module/kvm/parameters/halt_poll_ns'
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