Re: [Xen-devel] [PATCH v4 35/46] xen/sched: make vcpu_wake() and vcpu_sleep() core scheduling aware

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2019-09-27 at 09:00 +0200, Juergen Gross wrote:
> vcpu_wake() and vcpu_sleep() need to be made core scheduling aware:
> they might need to switch a single vcpu of an already scheduled unit
> between running and not running.
> 
> Especially when vcpu_sleep() for a vcpu is being called by a vcpu of
> the same scheduling unit special care must be taken in order to avoid
> a deadlock: the vcpu to be put asleep must be forced through a
> context switch without doing so for the calling vcpu. For this
> purpose add a vcpu flag handled in sched_slave() and in
> sched_wait_rendezvous_in() allowing a vcpu of the currently running
> unit to switch state at a higher priority than a normal schedule
> event.
> 
> Use the same mechanism when waking up a vcpu of a currently active
> unit.
> 
> While at it make vcpu_sleep_nosync_locked() static as it is used in
> schedule.c only.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>
I'm ok with the code in this patch.

I'd just like to see the comment(s) around the asymmetry between
vcpu_sleep_xxx() and vcpu_wake() added, as agreed upon this morning (in
the V3 thread).

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