Re: [Xen-devel] Question regarding Xen scheduler

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

> -----Original Message-----
> From: Dario Faggioli [mailto:dario.faggioli@xxxxxxxxxx]
> Sent: Friday, October 24, 2014 10:56 AM
> To: Jan Beulich
> Cc: Zytaruk, Kelly; Andrew Cooper; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Question regarding Xen scheduler
> 
> On Fri, 2014-10-10 at 09:12 +0100, Jan Beulich wrote:
> > >>> On 08.10.14 at 15:57, <andrew.cooper3@xxxxxxxxxx> wrote:
> > > On 08/10/14 14:05, Zytaruk, Kelly wrote:
> > >> 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.
> >
> > But I'd like to note that suggestions to add some mechanism to allow
> > this have been made more than once in the past.
> >
> And it does seems sensible, as a mechanism, at least IMO. However, the
> problem, as often in scheduling, especially when dealing with a complex
> architecture, such as Xen's one, would be how to use it "right"...
> Assuming we even know what "right" means in this case.
> 
> In fact, this is the typical thing that can bring a lot of benefits in one
> situation/workload, and at the same time disrupt substantially another one!
> :-/
> 
> For instance, Kelly, if I can ask, how where you thinking to use it, if it 
> were
> there?

I am thinking of the case where I have a sequence of hardware registers (can't 
be more specific yet at this point in time) that need to be accessed without 
being interrupted.  In some cases timing is critical and it can't start the 
sequence, be interrupt by a context switch and then wait until it gets its next 
time slice before continuing. 

Thanks,
Kelly
> 
> Regards,
> Dario
> 
> --
> <<This happens because I choose it to happen!>> (Raistlin Majere)
> -----------------------------------------------------------------
> Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software
> Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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