Re: [Xen-devel] Question regarding Xen scheduler

["Zytaruk, Kelly" <Kelly.Zytaruk@xxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Wednesday, October 08, 2014 9:57 AM
> To: Zytaruk, Kelly; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Question regarding Xen scheduler
> 
> 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

Thanks Andrew, with the exception of the last answer("> Not which comes to 
mind")  :-) that's exactly what I needed to know.  It helps a lot.

Kelly

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