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Date: Wed, 19 Jun 2013 15:53:49 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Magnus Damm <magnus.damm@...il.com>
CC: linux-kernel <linux-kernel@...r.kernel.org>,
Mark Rutland <mark.rutland@....com>,
SH-Linux <linux-sh@...r.kernel.org>,
Marc Zyngier <marc.zyngier@....com>,
Catalin Marinas <catalin.marinas@....com>,
"Simon Horman [Horms]" <horms@...ge.net.au>,
John Stultz <john.stultz@...aro.org>,
Shinya Kuribayashi <shinya.kuribayashi.px@...esas.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH/RFC] clockevents: Ignore C3STOP when CPUIdle is disabled
On 06/18/2013 10:56 AM, Magnus Damm wrote:
> Hi Daniel,
>
> On Tue, Jun 18, 2013 at 5:30 PM, Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>> On 06/18/2013 09:17 AM, Magnus Damm wrote:
>>> From: Magnus Damm <damm@...nsource.se>
>>>
>>> Introduce the function tick_device_may_c3stop() that
>>> ignores the C3STOP flag in case CPUIdle is disabled.
>>>
>>> The C3STOP flag tells the system that a clock event
>>> device may be stopped during deep sleep, but if this
>>> will happen or not depends on things like if CPUIdle
>>> is enabled and if a CPUIdle driver is available.
>>>
>>> This patch assumes that if CPUIdle is disabled then
>>> the sleep mode triggering C3STOP will never be entered.
>>> So by ignoring C3STOP when CPUIdle is disabled then it
>>> becomes possible to use high resolution timers with only
>>> per-cpu local timers - regardless if they have the
>>> C3STOP flag set or not.
>>>
>>> Observed on the r8a73a4 SoC that at this point only uses
>>> ARM architected timers for clock event and clock sources.
>>>
>>> Without this patch high resolution timers are run time
>>> disabled on the r8a73a4 SoC - this regardless of CPUIdle
>>> is disabled or not.
>>>
>>> The less short term fix is to add support for more timers
>>> on the r8a73a4 SoC, but until CPUIdle support is enabled
>>> it must be possible to use high resoultion timers without
>>> additional timers.
>>>
>>> I'd like to hear some feedback and also test this on more
>>> systems before merging the code, see the non-SOB below.
>>>
>>> Not-Yet-Signed-off-by: Magnus Damm <damm@...nsource.se>
>>> ---
>>>
>>> An earlier ARM arch timer specific version of this patch was
>>> posted yesterday as:
>>> "[PATCH/RFC] arm: arch_timer: Do not set C3STOP in case CPU_IDLE=n"
>>>
>>> Many thanks to Mark Rutland for his kind feedback.
>>>
>>> kernel/time/tick-broadcast.c | 8 ++++----
>>> kernel/time/tick-common.c | 2 +-
>>> kernel/time/tick-internal.h | 11 +++++++++++
>>> 3 files changed, 16 insertions(+), 5 deletions(-)
>>>
>>> --- 0001/kernel/time/tick-broadcast.c
>>> +++ work/kernel/time/tick-broadcast.c 2013-06-18 15:36:21.000000000 +0900
>>> @@ -71,7 +71,7 @@ int tick_check_broadcast_device(struct c
>>> if ((dev->features & CLOCK_EVT_FEAT_DUMMY) ||
>>> (tick_broadcast_device.evtdev &&
>>> tick_broadcast_device.evtdev->rating >= dev->rating) ||
>>> - (dev->features & CLOCK_EVT_FEAT_C3STOP))
>>> + tick_device_may_c3stop(dev))
>>> return 0;
>>>
>>> clockevents_exchange_device(tick_broadcast_device.evtdev, dev);
>>> @@ -146,7 +146,7 @@ int tick_device_uses_broadcast(struct cl
>>> * feature and the cpu is marked in the broadcast mask
>>> * then clear the broadcast bit.
>>> */
>>> - if (!(dev->features & CLOCK_EVT_FEAT_C3STOP)) {
>>> + if (!tick_device_may_c3stop(dev)) {
>>> int cpu = smp_processor_id();
>>> cpumask_clear_cpu(cpu, tick_broadcast_mask);
>>> tick_broadcast_clear_oneshot(cpu);
>>> @@ -270,7 +270,7 @@ static void tick_do_broadcast_on_off(uns
>>> /*
>>> * Is the device not affected by the powerstate ?
>>> */
>>> - if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP))
>>> + if (!dev || !tick_device_may_c3stop(dev))
>>> goto out;
>>>
>>> if (!tick_device_is_functional(dev))
>>> @@ -568,7 +568,7 @@ void tick_broadcast_oneshot_control(unsi
>>> td = &per_cpu(tick_cpu_device, cpu);
>>> dev = td->evtdev;
>>>
>>> - if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
>>> + if (!tick_device_may_c3stop(dev))
>>> return;
>>>
>>> bc = tick_broadcast_device.evtdev;
>>> --- 0001/kernel/time/tick-common.c
>>> +++ work/kernel/time/tick-common.c 2013-06-18 15:36:29.000000000 +0900
>>> @@ -52,7 +52,7 @@ int tick_is_oneshot_available(void)
>>>
>>> if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
>>> return 0;
>>> - if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
>>> + if (!tick_device_may_c3stop(dev))
>>> return 1;
>>> return tick_broadcast_oneshot_available();
>>> }
>>> --- 0001/kernel/time/tick-internal.h
>>> +++ work/kernel/time/tick-internal.h 2013-06-18 15:40:10.000000000 +0900
>>> @@ -141,6 +141,17 @@ static inline int tick_device_is_functio
>>> return !(dev->features & CLOCK_EVT_FEAT_DUMMY);
>>> }
>>>
>>> +/*
>>> + * Check, if the device has C3STOP behavior and CPU Idle is enabled
>>> + */
>>> +static inline bool tick_device_may_c3stop(struct clock_event_device *dev)
>>
>> I prefer tick_device_is_reliable(struct clock_event_device *dev).
>
> Sure. I took the name from the flag, thought that made it easy to follow.
>
> I wonder what the timekeeping maintainers prefer?
Personally, I would prefer tick_device_is_reliable function instead of
c3stop because this one is coming from the C-state Intel semantic. On
the other architectures, the C-state does not make sense and, especially
for ARM, you can have idle state corresponding to the index #1 where the
timer is shutdown. This comment also apply to CLOCK_EVT_FEAT_C3STOP ...
but this is diverging from the purpose of your patch.
>>> +{
>>> + /* The C3 sleep mode can only trigger when CPU Idle is enabled,
>>> + * so if CPU Idle is disabled then the C3STOP flag can be ignored */
>>> + return (IS_ENABLED(CONFIG_CPU_IDLE) &&
>>> + (dev->features & CLOCK_EVT_FEAT_C3STOP));
>>> +}
>>
>> Preferably you may use the format:
>>
>> #ifdef CONFIG_CPU_IDLE
>> static inline bool tick_device_is_reliable(struct clock_event_device *dev)
>> {
>> return dev->features & CLOCK_EVT_FEAT_C3STOP;
>> }
>> #else
>> static inline bool tick_device_is_reliable(struct clock_event_device *dev)
>> {
>> return true;
>> }
>> #endif
>>
>> to conform the header style format already present in the file.
>
> I agree with you about following the same style. Actually, I wrote
> the code to follow the code right above the function, but I decided to
> return bool instead of int. I don't mind so much in general though,
> except trying to keep the code at least half well-commented and
> relatively compact.
>
> So regarding stylistic things, sure, we can move around things.
> Question is just if this is acceptable or not. =)
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