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

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Message-ID: <alpine.DEB.2.10.1604061652410.31453@sstabellini-ThinkPad-X230>
Date:	Wed, 6 Apr 2016 16:53:54 -0700 (PDT)
From:	Stefano Stabellini <sstabellini@...nel.org>
To:	David Vrabel <dvrabel@...tab.net>
cc:	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	rt@...utronix.de, David Vrabel <david.vrabel@...rix.com>
Subject: Re: [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.
 
ARM guests behave like x86 PV guests in this regard. I expect the
comment to be appropriate for both archs or none.