Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

Anthony Liguori
2010-12-03T18:07:18Z

On 12/03/2010 11:58 AM, Chris Wright wrote:
> * Srivatsa Vaddagiri (vatsa@linux.vnet.ibm.com) wrote:
>
>> On Fri, Dec 03, 2010 at 09:29:06AM -0800, Chris Wright wrote:
>>
>>> That's what Marcelo's suggestion does w/out a fill thread.
>>>
>> There's one complication though even with that. How do we compute the
>> real utilization of VM (given that it will appear to be burning 100% cycles)?
>> We need to have scheduler discount the cycles burnt post halt-exit, so more
>> stuff is needed than those simple 3-4 lines!
>>
> Heh, was just about to say the same thing ;)
>

My first reaction is that it's not terribly important to account the
non-idle time in the guest because of the use-case for this model.

Eventually, it might be nice to have idle time accounting but I don't
see it as a critical feature here.

Non-idle time simply isn't as meaningful here as it normally would be.
If you have 10 VMs in a normal environment and saw that you had only 50%
CPU utilization, you might be inclined to add more VMs. But if you're
offering deterministic execution, it doesn't matter if you only have
"50%" utilization. If you add another VM, the guests will get exactly
the same impact as if they were using 100% utilization.

Regards,

Anthony Liguori

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