Re: [RFC] [Design] Better XL support of RTDS scheduler for Xen 4.6

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Tue, 2015-02-24 at 14:16 +0000, Ian Campbell wrote:
> On Tue, 2015-02-24 at 11:30 +0000, Dario Faggioli wrote:

> > Semantically speaking, they just should be killed. OTOH, what I was
> > suggesting was this: if one calls libxl_domain_sched_params_set(), which
> > takes a libxl_domain_sched_params, the budget and priod there will be
> > interpreted as "for the whole domain", and applied to all the domain's
> > vcpus. It's in this sense that I see it an either/or:
> >  - at domain creation time, if the user does not say anything we'll use
> >    the domain-wide API for setting a default budget and period for all
> >    the vcpus.
> >  - if the user does say something in the config file (once this will be
> >    possible), or upon request, via the proper xl command, to modify the
> >    parameters of vcpu X, we'll use the vcpu-wide API.
> 
> The simplest (and IMHO least surprising) thing would be to have the
> per-vcpu ones override the per-domain ones. 
>
I agree.

> So at build time you would first call the per-domain set function with
> whatever parameters were provided, followed by setting any per-vcpu
> options which are configured.
> 
Yep.

> At run time via xl commands I guess they would be separate commands for
> domains vs vcpus, 
>
Yes, either there will be separate commands, or the same command will
have a way of specifying whether the parameters are to be considered
domain-wide, or just apply to one (or more) vcpus.

Still using RTDS as an example, this is what I was suggesting, earlier
in this thread
(http://www.gossamer-threads.com/lists/xen/devel/368154#368154):

    # xl sched-rtds -d 4 -p 10000 -b 5000 
     | 
     ---> sets all the vcpus of domain 4 to 5000/10000 

    # xl sched-rtds -d 3 -v 2 -p 5000 -b 2000 
     | 
     ---> set vcpu 2 of domain 4 to 2000/5000 

    # xl sched-rtds -d 2 -v 0 -p 10000 -b 1000 -v 1 -p 5000 -b 2500 
     | 
     ---> set vcpu 0 of domain 2 to 1000/10000 and vcpu 1 of 
          domain 2 to 2500/5000 

> and if you call the per-domain one I'd probably expect
> it to clobber any existing per-vcpu settings (i.e act like the vcpu
> option given --all).
> 
Exactly

Regards,
Dario

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