Re: [Xen-devel] [PATCH v5 2/5] build: Hook the schedulers into Kconfig

[Jonathan Creekmore <jonathan.creekmore@xxxxxxxxx>]

Jan Beulich writes:

>>>> On 14.01.16 at 17:34, <ian.campbell@xxxxxxxxxx> wrote:
>> On Thu, 2016-01-14 at 10:23 -0600, Jonathan Creekmore wrote:
>>> Jan Beulich writes:
>>>
>>> > > > > On 14.01.16 at 15:49, <jonathan.creekmore@xxxxxxxxx> wrote:
>>> > > --- a/xen/common/Kconfig
>>> > > +++ b/xen/common/Kconfig
>>> > > @@ -51,4 +51,63 @@ config KEXEC
>>> > >
>>> > >           If unsure, say Y.
>>> > >
>>> > > +# Enable schedulers
>>> > > +menu "Schedulers"
>>> > > +       visible if EXPERT = "y"
>>> > > +
>>> > > +config SCHED_CREDIT
>>> > > +       bool
>>> > > +       default y
>>> > > +       ---help---
>>> > > +         The traditional credit scheduler is a general purpose
>>> > > scheduler.
>>> >
>>> > So is this option now useful for anything?
>>>
>>> It keeps the code between all of the schedulers consistent (all of them
>>> have a #define if they are compiled it)
>>
>> FWIW I think this (consistency) is a reasonable argument for having this
>> option even if it doesn't actually do anything.
>
> While I can see your point, I dislike useless clutter in .config (also
> on Linux, where I every once in a while send some cleanup
> patches).
>
>>> > > +choice
>>> > > +       prompt "Default Scheduler?"
>>> > > +       default SCHED_CREDIT_DEFAULT if SCHED_CREDIT
>>> > > +       default SCHED_CREDIT2_DEFAULT if SCHED_CREDIT2
>>> > > +       default SCHED_RTDS_DEFAULT if SCHED_RTDS
>>> > > +       default SCHED_ARINC653_DEFAULT if SCHED_ARINC653
>>> >
>>> > And certainly all these defaults are now pointless, considering
>>> > that the condition of the first one is "if y".
>>>
>>> Yes, I could rip all of those out now since credit is always the
>>> default. I left it in there for the ideal case that credit didn't have
>>> to be special cased but, at this point, I will rip it out if you want.
>>
>> What is the behaviour of the above set of "default"s if more than one of
>> the SCHED_* is enabled? Does it pick the first, last, one at random?
>
> The first for which the condition is true.

Absolutely correct. The first true condition is the one that is chosen.

>> If credit is now always the default I think that would be better expressed
>> with a single "default SCHED_CREDIT_DEFAULT".
>
> Indeed.

And that is what I have already done for a v6 that I am sitting on to
see if I get more review comments.

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