Re: [Xen-devel] [PATCH RFC v1 4/4] libxc for rt scheduler

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-07-17 at 16:34 +0100, George Dunlap wrote:
> On Thu, Jul 17, 2014 at 4:29 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Fri, 2014-07-11 at 16:49 +0200, Dario Faggioli wrote:
> >
> >> So, the bouncing logic seems fine. Looking at what other schedulers do,
> >> there should be no particular need for bouncing anything.
> >
> > Seems like there is some confusing precedent around the use of sysctl vs
> > domctl for sched parameters here.
> >
> > Most schedulers use domctl but arinc uses sysctl.
> 
> They're controlling different things.
> 
> domctl is controlling parameters related to *a particular domain* (for
> instance, weight or cap); sysctl is relating to setting parameters
> *for the scheduler as a whole* (for example, timeslice).

Ah, that makes sense.

It seems that arinc handles some degree of per-dom settings via the
sysctl interface though, since xen_sysctl_arinc653_schedule takes an
array of things which contain domid+vcpuid+params. Perhaps that's
peculiar to the way arinc works though. (Although it seems rather
incorrect to me for the array to be fixed size instead of a guest
handle...)

Lets not repeat that mistake with this new scheduler, if the domctl (or
a sysctl for that matter) needs per VCPU information then it should IMHO
take the parameters inline in the struct (like the others), anything
dynamic like the per-vcpu stuff should then be a GUEST_HANDLE pointer to
a dynamically sized array (accessed with copy_from_guest_offset et al).

Ian.


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