linux-kernel - Re: [PATCH 1/3] clockevents: Retry programming min delta up to 10 times

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Date:   Thu, 19 Oct 2017 14:21:23 +0100
From:   Matt Redfearn <matt.redfearn@...s.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        James Hogan <james.hogan@...s.com>,
        <linux-mips@...ux-mips.org>, James Hogan <jhogan@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] clockevents: Retry programming min delta up to 10
 times



On 19/10/17 13:43, Thomas Gleixner wrote:
> On Thu, 19 Oct 2017, Matt Redfearn wrote:
>>   	unsigned long long clc;
>>   	int64_t delta;
>> +	int i;
>>   
>> -	delta = dev->min_delta_ns;
>> -	dev->next_event = ktime_add_ns(ktime_get(), delta);
>> +	for (i = 0;;) {
> Bah. What's wrong with
>
> 	for (i = 0; i < 10; i++) {
>
> 	    	....
> 		if (!(dev->set_next_event((unsigned long) clc, dev))
> 			return 0;
> 	}
> 	return -ETIME;
>
> Hmm?

Sure, can make it like that.

>> +		delta = dev->min_delta_ns;
>> +		dev->next_event = ktime_add_ns(ktime_get(), delta);
>>   
>> -	if (clockevent_state_shutdown(dev))
>> -		return 0;
>> +		if (clockevent_state_shutdown(dev))
>> +			return 0;
>>   
>> -	dev->retries++;
>> -	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
>> -	return dev->set_next_event((unsigned long) clc, dev);
>> +		dev->retries++;
>> +		clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
> I'd rather make that:
>
> 	delta = 0;
> 	for (i = 0; i < 10; i++) {
> 		delta += dev->min_delta_ns;
> 		dev->next_event = ktime_add_ns(ktime_get(), delta);
> 		clc = .....
> 	   	.....
>
> That makes it more likely to succeed fast. Hmm?

That will set the target time to increasing multiples of min_delta_ns in 
the future, right? Sure, it should make it succeed faster - I'll make it 
like that. Are you OK with the arbitrarily chosen 10 retries?

Thanks,
Matt

>
> Thanks,
>
> 	tglx