Re: [PATCH 3 of 3] full support of setting scheduler parameters on domain creation

[Dario Faggioli <raistlin@linux.it>]

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On Tue, 2012-05-22 at 14:39 +0200, Juergen Gross wrote:
> > This interface really makes libxl_sched_params differ from all the other
> > libxl structs (which have a public _init function and an internal
> > setdefaults function). I'm not really sure its justified either, I was
> > under the impression that you'd found that there were useful
> > discriminating values?
> 
> Dario opted for this solution, so I proposed a patch implementing it.
> I prefer this solution, too, as it isn't exporting scheduler internals to
> the tools.
> 
Yep. I agree with Ian that having two different procedures for the first
as compared to the subsequent operations on the scheduling parameters is
bad, but still, as a matter of my personal taste, I'd prefer no to have
things belonging to the hypervisor/scheduler replicated in the
toolstack, although they're just simple default values. It's still
something you need to always remember to check for consistency, or bad
things will happen! :-/

However, Ian's approach seems clean and nice as well, and I'm not really
sure which one I like most, so don't count me when deciding, I'm fine
with both.

> >>   int libxl__sched_set_params(libxl__gc *gc, uint32_t domid,
> >> libxl_sched_params *scparams)
> >>   {
> >>       libxl_ctx *ctx = libxl__gc_owner(gc);
> >> -    libxl_scheduler sched;
> >>       libxl_sched_sedf_domain sedf_info;
> >>       libxl_sched_credit_domain credit_info;
> >>       libxl_sched_credit2_domain credit2_info;
> >>       int ret;
> >>
> >> -    sched = libxl_get_scheduler (ctx);
> >> -    switch (sched) {
> >> +    switch (scparams->sched) {
> > What happens if scparams->sched is not the scheduler used for this
> > domain? Should it either be checked or set somewhere?
> 
> The check would be the same as the original setting of scparams->sched.
> Setting of the scheduler parameters will be rejected by the hypervisor if the
> scheduler does not match.
> 
I was thinking this should go through finding out what domid's cpupool
is and then checking that scheduler, as it is being done somewhere
else... Isn't this the case?

Regards,
Dario

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


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