With PowerKVM, exits from KVM to qemu are even more expensive than on
x86. One significant source of these we're finding (since we usually
work in -nographic mode) is the nographic_timer.
At present, we're using a hack to disable it, but that's obviously not
a long term solution. From examination, it looks like the only
purpose of this timer is to flush coalesced mmios. So it seems like
the timer should only be activated when a coalesced mmio region
actually exists, but I'm not entirely sure how to go about that.
Thinking longer term, it seems very odd that a userspace periodic
timer handles this at all. Surely it would make more sense to use a
kernel timer within KVM, which can be activated only when there are
actually pending coalesced MMIOs in the buffer.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
