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

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On 12/03/2010 11:58 AM, Chris Wright wrote:
* Srivatsa Vaddagiri (vatsa@xxxxxxxxxxxxxxxxxx) 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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