Subject: Re: [PATCH] KVM: PPC: Don't sync timebase when inside KVM

From: Scott Wood <[email-masked]>
Date: Wed, 29 Feb 2012 13:06:05 -0600

On 02/29/2012 12:28 PM, Alexander Graf wrote:
> 
> 
> On 29.02.2012, at 18:50, Scott Wood <[email-masked]> wrote:
> 
>> On 02/28/2012 08:16 PM, Alexander Graf wrote:
>>> When we know that we're running inside of a KVM guest, we don't have to
>>> worry about synchronizing timebases between different CPUs, since the
>>> host already took care of that.
>>>
>>> This fixes CPU overcommit scenarios where vCPUs could hang forever trying
>>> to sync each other while not being scheduled.
>>>
>>> Reported-by: Stuart Yoder <[email-masked]>
>>> Signed-off-by: Alexander Graf <[email-masked]>
>>
>> This should apply to any hypervisor, not just KVM.  
> 
> Sure, but do you have a generic function to evaluate that? :)

The presence of a hypervisor node without testing compatible.  Might not
get them all, but at least it will cover more than just KVM.

>> Which platforms are you seeing this on?  If it's on Freescale chips,
>> U-Boot should be doing the sync and Linux should never do it, even in
>> the absence of a hypervisor.
> 
> This is on e500mc.

On e500mc Linux should never by trying to sync the timebase.  If it is,
let's fix that.

-Scott