Re: [Xen-users] cpufreq problems with hvm

[Birger Brunswiek <birger.b@xxxxxxx>]

Tian, Kevin wrote:
> > From: Birger Brunswiek
> > Sent: 2008å7æ24æ 4:58
> >
> > Hi all,
> > I was wondering if cpu frequency scaling in dom0 (using the 
> > cpufreq=dom0-kernel 
> > boot parameter) may cause problems with HVM domUs? This is on 
> > Xen 3.2.1.
> > PV domUs seem to work just fine. They adjust to the frequency 
> > change on the go. 
> > The HVM I run using the unmodified_driver drivers (also from 
> > the 3.2.1 release) 
> > seem to have very slow timers if dom0 lowers the frequency.
> Current HVM can't cope with freq/tsc change, unless all rdtsc
> are trapped which then may bring other side-effects for heavy
> overhead. It's better for you to try cpufreq on a platform with
> constant TSC, e.g. any Intel processors supporting VT.
I see ... it's just when the last time I looked for Intel CPUs it way quite 
difficult to get those with VT in the consumer segment. That's quite different 
with AMD.
Does anyone know if the modules (?) which are responsible to get the freq 
scaling right in PVs can be used/ported to an HVM? Similar to the unmodified 
drivers to use a paravirtualised disk and netif.
Birger

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