Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 21 May 2021 12:25:04 +0100
From:   Will Deacon <will@kernel.org>
To:     Mika =?iso-8859-1?Q?Penttil=E4?= <mika.penttila@nextfour.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Lorenzo Colitti <lorenzo@google.com>,
        John Stultz <john.stultz@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>, kernel-team@android.com
Subject: Re: [PATCH 3/5] tick/broadcast: Prefer per-cpu oneshot wakeup timers
 to broadcast
Message-ID: <20210521112503.GA11850@willie-the-truck>
References: <20210520184705.10845-1-will@kernel.org>
 <20210520184705.10845-4-will@kernel.org>
 <a269c869-b966-75d5-5fe1-6ed6921c1b83@nextfour.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <a269c869-b966-75d5-5fe1-6ed6921c1b83@nextfour.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Fri, May 21, 2021 at 05:25:41AM +0300, Mika Penttil? 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.

Will