Re: [Xen-devel] [PATCH 54/60] xen/sched: add minimalistic idle scheduler for free cpus

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Tue, 2019-05-28 at 12:33 +0200, Juergen Gross wrote:
> Instead of having a full blown scheduler running for the free cpus
> add a very minimalistic scheduler for that purpose only ever
> scheduling
> the related idle vcpu. This has the big advantage of not needing any
> per-cpu, per-domain or per-scheduling unit data for free cpus and in
> turn simplifying moving cpus to and from cpupools a lot.
> 
> As this new scheduler is not user selectable don't register it as an
> official scheduler, but just include it in schedule.c.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V1: new patch
> ---

> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -83,6 +83,57 @@ extern const struct scheduler
> *__start_schedulers_array[], *__end_schedulers_arr
>  
>  static struct scheduler __read_mostly ops;
>  
> [...]
>
> +static void *
> +sched_idle_alloc_vdata(const struct scheduler *ops, struct
> sched_unit *unit,
> +                       void *dd)
> +{
> +    /* Any non-NULL pointer is fine here. */
> +    return (void *)1UL;
> +}
> +
I think the proper thing to do, here, would be to convert alloc_vdata()
to PTR_ERR() & IS_ERR().

That's another patch, of course, and given that this series is rather
big already, I'm not sure about asking for it to be done in the context
of this work.

I can do it myself, either right now or after this series is merged
(for the sake of not making rebasing 60 patches more complicated than
it must be already, for you :-D).

Let me know what you think.

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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