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Date: Thu, 27 Sep 2012 14:04:15 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai] [PATCH 1/2] Refactor ipipe_select_timers
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To: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Cc: "Kiszka, Jan" <jan.kiszka@siemens.com>, "xenomai@xenomai.org" <xenomai@xenomai.org>

On 09/27/2012 10:28 AM, Wolfgang Mauerer wrote:
> On 26/09/12 23:28, Gilles Chanteperdrix wrote:
>> On 09/26/2012 03:16 PM, Wolfgang Mauerer wrote:
>>
>>> Make the control flow more readable. No functional changes.
>>>
>>> Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
>>> ---
>>>  kernel/ipipe/timer.c |   82 +++++++++++++++++++++++++++++++------------------
>>>  1 files changed, 52 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/kernel/ipipe/timer.c b/kernel/ipipe/timer.c
>>> index 8b2eb6f..765340e 100644
>>> --- a/kernel/ipipe/timer.c
>>> +++ b/kernel/ipipe/timer.c
>>> @@ -154,21 +154,55 @@ static void ipipe_timer_request_sync(void)
>>>  	timer->request(timer, steal);
>>>  }
>>>  
>>> +/* Set up a timer as per-cpu timer for ipipe */
>>> +static int install_pcpu_timer(unsigned cpu, unsigned hrclock_freq,
>>> +			      struct ipipe_timer *t) {
>>> +	unsigned hrtimer_freq;
>>> +	unsigned long long tmp;
>>> +
>>> +#ifdef CONFIG_GENERIC_CLOCKEVENTS
>>> +	struct clock_event_device *evtdev;
>>> +	evtdev = t->host_timer;
>>> +
>>> +	if (evtdev && evtdev->mode == CLOCK_EVT_MODE_SHUTDOWN)
>>> +		return 0;
>>> +#endif /* CONFIG_GENERIC_CLOCKEVENTS */
>>> +
>>> +	if (__ipipe_hrtimer_freq == 0)
>>> +		__ipipe_hrtimer_freq = t->freq;
>>> +
>>> +	per_cpu(ipipe_percpu.hrtimer_irq, cpu) = t->irq;
>>> +	per_cpu(percpu_timer, cpu) = t;
>>> +
>>> +	hrtimer_freq = t->freq;
>>> +	if (__ipipe_hrclock_freq > UINT_MAX)
>>> +		hrtimer_freq /= 1000;
>>> +
>>> +	t->c2t_integ = hrtimer_freq / hrclock_freq;
>>> +	tmp = (((unsigned long long)
>>> +		(hrtimer_freq % hrclock_freq)) << 32)
>>> +		+ hrclock_freq - 1;
>>> +	do_div(tmp, hrclock_freq);
>>> +	t->c2t_frac = tmp;
>>> +
>>> +	return 1;
>>> +}
>>> +
>>> +
>>>  /*
>>> - * choose per-cpu timer: we walk the list, and find the timer with the
>>> - * highest rating.
>>> + * Choose per-cpu timers with the highest rating by traversing the
>>> + * rating-sorted list for each CPU.
>>>   */
>>>  int ipipe_select_timers(const struct cpumask *mask)
>>>  {
>>> -	struct clock_event_device *evtdev;
>>> -	unsigned hrclock_freq, hrtimer_freq;
>>> +	unsigned hrclock_freq;
>>>  	unsigned long long tmp;
>>>  	struct ipipe_timer *t;
>>>  	unsigned long flags;
>>> -	unsigned cpu, khz;
>>> +	unsigned cpu;
>>> +	bool found;
>>>  
>>> -	khz = __ipipe_hrclock_freq > UINT_MAX;
>>> -	if (khz) {
>>> +	if (__ipipe_hrclock_freq > UINT_MAX) {
>>>  		tmp = __ipipe_hrclock_freq;
>>>  		do_div(tmp, 1000);
>>>  		hrclock_freq = tmp;
>>> @@ -177,34 +211,22 @@ int ipipe_select_timers(const struct cpumask *mask)
>>>  
>>>  	spin_lock_irqsave(&lock, flags);
>>>  	for_each_cpu(cpu, mask) {
>>> +		found = false;
>>>  		list_for_each_entry(t, &timers, link) {
>>>  			if (!cpumask_test_cpu(cpu, t->cpumask))
>>>  				continue;
>>>  
>>> -			evtdev = t->host_timer;
>>> -#ifdef CONFIG_GENERIC_CLOCKEVENTS
>>> -			if (!evtdev
>>> -			    || evtdev->mode != CLOCK_EVT_MODE_SHUTDOWN)
>>> -#endif /* CONFIG_GENERIC_CLOCKEVENTS */
>>> -				goto found;
>>> +			if (install_pcpu_timer(cpu, hrclock_freq, t)) {
>>> +				found = true;
>>
>>
>> Talking about readability, I find a goto with a clear label name much
>> more readable than a flag. So, NACK this patch, please keep the goto.
>  
> So you're against the refactoring, or only against using the flag?
> Keeping the goto leads to something like
> 
> 	if (install_pcpu_timer(cpu, hrclock_freq, t))
> 		goto found
> (...)
> found:    ;
> 
> since we need a statement for the label, but nothing is left to do.
> I find this fairly ugly, but if you prefer it over a flag, then
> so be it.

Then use return instead of goto...

-- 
					    Gilles.