Re: [patch 4/4] KVM: allow direct access to PMTimer port

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> On Sun, May 25, 2008 at 03:31:03PM +0300, Avi Kivity wrote:
>   
>> Marcelo Tosatti wrote:
>>     
>>> There's not much point in exiting for pmtimer reads, since it runs at a
>>> fixed clock rate and its start value is undefined.
>>>  
>>>       
>> On a migration farm with lots of different hardware, eventually all 
>> guests will have migrated and none of them will be able to use the 
>> passthrough port.
>>
>> What about emulating pmtimer in the host kernel instead of userspace?  
>> It increases the hit from 1 exit to 3 exits, but they're much faster exits.
>>     
>
> I agree, even began writing it, but I think the non-passthrough case
> could be optimized later.
>   

But, I claim above that the passthrough case will never be in use on 
long-running guests due to migration.

-- 
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