Re: [Xen-devel] Question regarding Xen scheduler

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/10/14 14:05, Zytaruk, Kelly wrote:
> I would like to ask a question as to how the Xen scheduler handles certain 
> situations.  
> From everything that I have read I understand that the scheduler treats Dom0 
> just like any other DomU in regards to scheduling.

Correct.  (XenServer has a tweak which allows dom0's credit to scale
relative to current system load, but nothing more complicated.)

>
> My question is in regards to interrupt handlers, critical sections and kernel 
> code.  Is the Xen scheduler aware of whether the Dom0 is executing in kernel 
> code versus user mode code?  Can Dom0 kernel mode code be interrupted by the 
> Xen scheduler and then a DomU run for a while before returning back to Dom0 
> kernel mode code?

All domains may be interrupted by Xen.  Xen itself knows whether the
domain is in kernel or user mode, but the scheduler does not. 

>
> What about interrupt handling routines either in Dom0 or DomU.  Can a Task 
> switch to another DomU / Dom0 occur if in the middle of an interrupt handler?

Yes

>
> What if I am doing something time critical or sequence critical that can't be 
> interrupted?  Is there a way to tell the Xen scheduler that "I am in a 
> critical section and can't be interrupted by another Dom" so that Xen won't 
> task switch until I am done?

No.

>
> Other than reading the source code is there a good reference that I can read 
> for Xen internal details and architecture?  

Not which comes to mind.

~Andrew


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