linux-kernel - Re: [PREEMPT-RT] [Xen-devel] [PATCH] xen: Add comment for missing FROZEN notifier transitions

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Date:	Wed, 6 Apr 2016 16:08:50 +0200 (CEST)
From:	Anna-Maria Gleixner <anna-maria@...utronix.de>
To:	David Vrabel <dvrabel@...tab.net>
cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	David Vrabel <david.vrabel@...rix.com>, rt@...utronix.de,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PREEMPT-RT] [Xen-devel] [PATCH] xen: Add comment for missing
 FROZEN notifier transitions

On Wed, 6 Apr 2016, David Vrabel wrote:

> On 04/04/16 13:32, Anna-Maria Gleixner wrote:
> > Xen guests do not offline/online CPUs during suspend/resume and
> > therefore FROZEN notifier transitions are not required. Add this
> > explanation as a comment in the code to get not confused why
> > CPU_TASKS_FROZEN masked transitions are not considered.
> > 
> > Cc: David Vrabel <david.vrabel@...rix.com>
> > Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > Cc: xen-devel@...ts.xenproject.org 
> > Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> > ---
> >  arch/arm/xen/enlighten.c         |    6 ++++++
> >  arch/x86/xen/enlighten.c         |    7 +++++++
> >  drivers/xen/events/events_fifo.c |    6 ++++++
> >  3 files changed, 19 insertions(+)
> > 
> > --- a/arch/arm/xen/enlighten.c
> > +++ b/arch/arm/xen/enlighten.c
> > @@ -213,6 +213,12 @@ static int xen_cpu_notification(struct n
> >  				unsigned long action,
> >  				void *hcpu)
> >  {
> > +	/*
> > +	 * Xen guests do not offline/online CPUs during
> > +	 * suspend/resume, thus CPU_TASKS_FROZEN masked transitions
> > +	 * are not considered.
> > +	 */
> 
> This may not be true for arm guests.

Ok. Should the frozen transitions be handled the same way than the
corresponding non frozen transitions? If yes and if it doesn't matter
to mask action with ~CPU_TASKS_FROZEN in arch/x86/xen/enlighten.c and
drivers/xen/events/events_fifo.c like Juergen sugessts, I could change
the patch by masking action.

Anna-Maria