On 21.04.17 12:02, Paolo Bonzini wrote:
On 12/04/2017 18:29, Michael S. Tsirkin wrote:
I don't really agree we do not need the PV flag. mwait on kvm is
different from mwait on bare metal in that you are heavily penalized by
scheduler for polling unless you configure the host just so.
HLT lets you give up the host CPU if you know you won't need
it for a long time.
So while many people can get by with monitor cpuid (those that isolate
host CPUs) and it's a valuable option to have, I think a PV flag is also
a valuable option and can be set for more configurations.
Guest has an idle driver calling mwait on short waits and halt on longer
ones. I'm in fact testing an idle driver using such a PV flag and will
post when ready (after vacation ~3 weeks from now probably).
For now I think I'm removing the PV flag, making this just an
optimization of commit 87c00572ba05aa8c ("kvm: x86: emulate
monitor and mwait instructions as nop").
We can add it for 4.13 together with the idle driver.
I think that's a perfectly reasonable approach, yes. We can always add
the PV flag with the driver.
Thanks a lot!
Alex
