linux-kernel - Re: [PATCH 1/2] time: Serialize calls to 'clockevents_update

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Date:	Thu, 12 Dec 2013 13:07:45 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] time: Serialize calls to 'clockevents_update_freq'
 in the timing core

On 12/11/2013 09:09 PM, Sören Brinkmann wrote:
> Hi Daniel,
>
> On Wed, Dec 11, 2013 at 03:32:57PM +0100, Daniel Lezcano wrote:
>> On 12/10/2013 01:34 AM, Soren Brinkmann wrote:
>>> From: Thomas Gleixner <tglx@...utronix.de>
>>>
>>> We can identify the broadcast device in the core and serialize all
>>> callers including interrupts on a different CPU against the update.
>>> Also, disabling interrupts is moved into the core allowing callers to
>>> leave interrutps enabled when calling clockevents_update_freq().
>>>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
>>> ---
>>>   kernel/time/clockevents.c    | 29 ++++++++++++++++++++++-------
>>>   kernel/time/tick-broadcast.c | 25 +++++++++++++++++++------
>>>   kernel/time/tick-internal.h  |  4 ++++
>>>   3 files changed, 45 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
>>> index 086ad6043bcb..641d91003a45 100644
>>> --- a/kernel/time/clockevents.c
>>> +++ b/kernel/time/clockevents.c
>>> @@ -439,6 +439,16 @@ void clockevents_config_and_register(struct clock_event_device *dev,
>>>   }
>>>   EXPORT_SYMBOL_GPL(clockevents_config_and_register);
>>>
>>> +int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
>>> +{
>>> +	clockevents_config(dev, freq);
>>> +
>>> +	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
>>> +		return 0;
>>> +
>>> +	return clockevents_program_event(dev, dev->next_event, false);
>>> +}
>>> +
>>
>> ./arch/arm/kernel/smp_twd.c should be modified to call
>> __clockevents_update_freq instead of clockevents_update_freq, no ?
>
> IIUC, the __-version is only for timer core internal usage and not an
> exported interface. Doesn't the non-__ version work for the twd?
> I don't see issues on my Zynq platform with these patches.

I don't think there is an issue but if we can rid of the extra code 
added in clockevents_update_freq with this patch for twd, it would make 
sense. The __-version means the function is lockless and there is a 
function without '__' in the name with the lock.

> Another side note regarding the twd: Shouldn't we set the
> CLOCK_EVT_FEAT_PERCPU flag we introduced recently for that timer?

Yes.

There will be some fun with the patchset http://lwn.net/Articles/566270/ 
where the local timer could be used as a broadcast timer.


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