Re: [PATCH 3/5] tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast

[Will Deacon]

On Fri, May 21, 2021 at 12:25:03PM +0100, Will Deacon wrote:
> On Fri, May 21, 2021 at 05:25:41AM +0300, Mika Penttilä wrote:
> > On 20.5.2021 21.47, Will Deacon wrote:
> > >   /*
> > >    * Conditionally install/replace broadcast device
> > >    */
> > > -void tick_install_broadcast_device(struct clock_event_device *dev)
> > > +void tick_install_broadcast_device(struct clock_event_device *dev, int cpu)
> > >   {
> > >   	struct clock_event_device *cur = tick_broadcast_device.evtdev;
> > > +	if (tick_set_oneshot_wakeup_device(dev, cpu))
> > > +		return;
> > > +
> > >   	if (!tick_check_broadcast_device(cur, dev))
> > >   		return;
> > 
> > Does this disable hpet registering as a global broadcast device on x86 ? I
> > think it starts with cpumask = cpu0 so it qualifies for a percpu wakeup
> > timer.
> 
> Well spotted, I think you're probably right. I'll try to reproduce on my
> laptop to confirm, but I hadn't noticed the tricks played with the cpumask
> on x86.
> 
> I'll probably need to rework things so that we install the broadcast timer
> first, but prefer global devices.

... and in doing that, I noticed my module refcounting is off as well so
I'll definitely be spinning a v2.

Will