On 06/03/2014 04:21 PM, Gabriel L. Somlo wrote:
On Tue, Jun 03, 2014 at 11:17:48AM +0200, Paolo Bonzini wrote:
I think it's fine as it is now. :)
On Mon, Jun 02, 2014 at 09:55:18PM -0400, Gabriel L. Somlo wrote:
W.r.t. monitor/mwait, a guest can do one of the following:
1. Never check CPUID, and never use monitor/mwait
- This is great, we don't have to do anything about these
2. Check CPUID for mwait, use it to idle in preference over hlt
- Linux, Windows, and Mavericks (10.9) do this
- we never want to have CPUID say "yes" to these, since
monitor/mwait support will be clunky in the best case,
and hlt is overwhelmingly preferable! [*]
3. Never check CPUID, use monitor/mwait with abandon
- OS X 10.6 .. 10.8 does this
- emulating monitor/mwait here allows us to boot the guest
and use it, and perform sysadmin surgery to force a hlt
based idle
4. Check CPUID, panic if unavailable
- OS X 10.5 did this, IIRC.
- whether I can do kext surgery and get it to stop checking
CPUID *in addition to* falling back to hlt-based idle is
TBD.
- emulating monitor/mwait allows us to boot this type of
guest, BUT WE ALSO HAVE TO ADVERTISE IT VIA CPUID !!!
As it is right now, #4 is not being addressed (and we can't just
advertise mwait via cpuid, or we'd be screwing up #2).
I think we should be able to handle #4 by doing -cpu core2duo,+monitor
on the QEMU command line which should override the cpuid bits that the
kernel tells us.
Alex
I also feel a bit weird about the "undocumented feature" aspect
of NOT generating an invalid opcode for something that *should*
be an invalid opcode according to the feature set advertised via
cpuid...
So if there's a way to make it so we can tell QEMU/KVM to
"--enable-mwait" on a per-guest basis, I think that'd be better
than an always-on "undocumented" behavior...
But then again, I'm most likely missing something about the big
picture... :)
Thanks much,
--Gabriel
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