[vbox-dev] About Virtual Box VM Scheduling mechanism

Nikolay Igotti Nikolay.Igotti at Sun.COM
Sun Jul 4 23:49:04 PDT 2010


Chris is correct that VM mostly executed in regular OS thread (called 
EMT - emulation thread), things gets somewhat non-trivial when we talk 
about priveledged guest execution. Guest R0 code is executed in 
virtualized R0 (technically, in host kernel, inside ioctl() performed by 
EMT), and in sense, R0 code has its own preemption mechanism (details 
depends on virtualization technology used). Device emulation code is 
also partially in R0, but probably not of much relevance here.
Guest SMP spawns multiple threads of execution (thus can use multiple 
physical CPUs), and they interact via emulated interrupt controller (APIC)
and indirectly via shared resources locks (such as device lock).
Is there any specific problem you see?


Christian Pötzsch пишет:
> Hi,
> AFAIK, there is one EMT thread per VM and as different VM's are 
> executed as different processes they are scheduled by the host OS 
> scheduler. In the SMP case is more than one EMT thread, but these 
> threads are schedules by the OS as well.
> I will resent this to the dev mailing list, cause there are people 
> which know that stuff much more. Please ask and answer there.
> Christian
> On 7/2/10 7:19 AM, Suk Kyu Lee wrote:
>> Hello,
>> My name is Suk Kyu Lee and I’m a graduate research assistant at Korea
>> University.
>> I’m currently doing a research regarding about virtualization and was
>> using the VirtualBox OSE 3.1.6.
>> I was wondering if it is possible to know the general idea of the how
>> the VM scheduling mechanism within the Virtual Box.
>> I was having some problem with the code and it appears that there are
>> EMT thread within each VM, but couldn’t find the location within the
>> code regarding about how the VMM schedules the VM.
>> Thank you.
>> Sincerely,
>> Suk Kyu Lee

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