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From: Thomas Gleixner <tglx@linutronix.de>
To: "Will Deacon" <will@kernel.org>,
	"Mika Penttilä" <mika.penttila@nextfour.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Frederic Weisbecker <fweisbec@gmail.com>,
	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
Date: Fri, 21 May 2021 15:49:39 +0200	[thread overview]
Message-ID: <87tumw9oy4.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210521112503.GA11850@willie-the-truck>

On Fri, May 21 2021 at 12:25, 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.

HPET has cpumask(0) but does not have CLOCK_EVT_FEAT_PERCPU set. The
feature flag is a clear indicator for per cpu.

Thanks,

        tglx

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: "Will Deacon" <will@kernel.org>,
	"Mika Penttilä" <mika.penttila@nextfour.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Frederic Weisbecker <fweisbec@gmail.com>,
	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
Date: Fri, 21 May 2021 15:49:39 +0200	[thread overview]
Message-ID: <87tumw9oy4.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210521112503.GA11850@willie-the-truck>

On Fri, May 21 2021 at 12:25, 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.

HPET has cpumask(0) but does not have CLOCK_EVT_FEAT_PERCPU set. The
feature flag is a clear indicator for per cpu.

Thanks,

        tglx

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  parent reply	other threads:[~2021-05-21 13:49 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20 18:47 [PATCH 0/5] tick/broadcast: Allow per-cpu timers to be used instead of broadcast Will Deacon
2021-05-20 18:47 ` Will Deacon
2021-05-20 18:47 ` [PATCH 1/5] tick/broadcast: Drop unneeded CONFIG_GENERIC_CLOCKEVENTS_BROADCAST guard Will Deacon
2021-05-20 18:47   ` Will Deacon
2021-05-20 18:47 ` [PATCH 2/5] tick/broadcast: Split __tick_broadcast_oneshot_control() into a helper Will Deacon
2021-05-20 18:47   ` Will Deacon
2021-05-20 18:47 ` [PATCH 3/5] tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast Will Deacon
2021-05-20 18:47   ` Will Deacon
2021-05-21  2:25   ` Mika Penttilä
2021-05-21  2:25     ` Mika Penttilä
2021-05-21 11:25     ` Will Deacon
2021-05-21 11:25       ` Will Deacon
2021-05-21 12:18       ` Will Deacon
2021-05-21 12:18         ` Will Deacon
2021-05-21 13:49       ` Thomas Gleixner [this message]
2021-05-21 13:49         ` Thomas Gleixner
2021-05-21 14:43         ` Will Deacon
2021-05-21 14:43           ` Will Deacon
2021-05-20 18:47 ` [PATCH 4/5] tick/broadcast: Program wakeup timer when entering idle if required Will Deacon
2021-05-20 18:47   ` Will Deacon
2021-05-20 18:47 ` [PATCH 5/5] timer_list: Print name of per-cpu wakeup device Will Deacon
2021-05-20 18:47   ` Will Deacon

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