Re: [PATCH] xen/sched: fix get_cpu_idle_time() for smt=0 suspend/resume

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Wed, 2021-08-18 at 12:21 +0200, Juergen Gross wrote:
> Fix that by letting get_cpu_idle_time() deal with this case.
> 
> Fixes: 132cbe8f35632fb2 ("sched: fix get_cpu_idle_time() with core
> scheduling")
> Reported-by: Marek Marczykowski-Górecki
> <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Tested-by: Marek Marczykowski-Górecki
> <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
>
Mmm... This is an interesting one. In fact, this fix is not only
correct, it's also simple, effective and (I guess) easy enough to
backport.

Considering all these things together with the fact that we have an
open issue, I'm going to provide my:

Acked-by: Dario Faggioli <dfaggioli@xxxxxxxx>

(and this remains valid with Jan's proposed change done upon
committing.)

That said, in the long run...

> ---
> An alternative way to fix the issue would be to keep the
> sched_resource
> of offline cpus allocated like we already do with idle vcpus and
> units.
> This fix would be more intrusive, but it would avoid similar other
> bugs
> like this one.
> 
... it would be probably interesting to go this route, as it looks both
more consistent and future proof (I mean implement it proactively,
independently of issues... when/if we have time, of course!)

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