lkml.org 
[lkml]   [2011]   [Dec]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch 0/3] kvm tool: Serial emulation overhaul
On Tue, 13 Dec 2011, Avi Kivity wrote:
> On 12/13/2011 03:52 PM, Thomas Gleixner wrote:
> > On Tue, 13 Dec 2011, Avi Kivity wrote:
> > > Run your guest with x2apic enabled, the timing will be very different.
> >
> > And what magic do I have to use to make that happen other than having
> > x2apic support enabled in the kernel? Or do I need a certain kernel
> > version for host and guest to make that work?
>
> With qemu, -cpu host or -cpu blah,+x2apic. kvm-tool does the equivalent

Well, that was a trace from qemu-kvm (your latest tree). Now with -cpu
host it works and I get the same results as with kvm tool.

> of -cpu host, so I'm surprised it doesn't show up. x2apic has been
> recognized by the guest for a long time (ce69a784; 2.6.32, I'll be
> surprised if you have anything older than that on your machine).
>
> Does x2apic show up in your guest's /proc/cpuinfo?

Now it does :)

> > The whole APIC timer calibration and the back and forth
> > conversion is definitely nothing which falls into the category of
> > smart.
>
> APIC timer calibration is silly but it hasn't proven to be a real-world
> problem.

Well, that depends on the world. The issue with that calibration is
that it can be off and for a certain category of application it
matters. Definitely not for the usual virt workload stuff. But saving
cycles for highres/nohz enabled guests would be nice. Maybe I have a
go when I find a some time.

Thanks,

tglx


\
 
 \ /
  Last update: 2011-12-13 15:53    [W:0.194 / U:0.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site