Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

Nadav Amit
2017-03-21T17:29:32Z

> On Mar 21, 2017, at 9:58 AM, Radim Krčmář <rkrcmar@redhat.com> wrote:

> In '-smp 2', the writing VCPU always does 10000 wakeups by writing into
> monitored memory, but the mwaiting VCPU can be also woken up by host
> interrupts, which might add a few exits depending on timing.
>
> I didn't spend much time in making the PASS/FAIL mean much, or ensuring
> that we only get 10000 wakeups ... it is nothing to be worried about.
>
> Hint 240 behaves as nop even on my system, so I still don't find
> anything insane on that machine (if OS X is exluded) ...

From my days in Intel (10 years ago), I can say that MWAIT wakes for many
microarchitecural events beside interrupts.

Out of curiosity, aren’t you worried that on OS X the wbinvd causes an exit
after the monitor and before the mwait?