linux-kernel - Re: [PATCH v2 1/2] posix-timers: Prevents overrun counter overflow

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Date:	Sat, 24 Jan 2015 20:14:45 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Church <dchurch@...plus.com>
cc:	linux-kernel@...r.kernel.org, libc-alpha@...rceware.org
Subject: Re: [PATCH v2 1/2] posix-timers: Prevents overrun counter overflow

On Sat, 24 Jan 2015, Daniel Church wrote:
> +/*
> + * Updates a timer's overrun count while capping it to delaytimer_max
> + */
> +static void posix_timer_update_overrun_count(struct k_itimer *timer,
> +					     unsigned int overruns)
> +{
> +	const bool newOverrunsAboveMax = overruns >= delaytimer_max;
> +	const bool totalOverrunsAboveMax =
> +		timer->it_overrun >= 0 &&
> +		timer->it_overrun >= delaytimer_max - overruns;

No CaMelCaSe please. And the const here is pointless.

Aside of that in a function like this we really want short local
variables so we can avoid the horrible to read multi line code.

> +	if (newOverrunsAboveMax || totalOverrunsAboveMax) {
> +		timer->it_overrun = delaytimer_max;
> +	} else {
> +		timer->it_overrun += overruns;
> +	}
> +}
> +
>  /* Get clock_realtime */
>  static int posix_clock_realtime_get(clockid_t which_clock, struct timespec *tp)
>  {
> @@ -350,14 +370,17 @@ __initcall(init_posix_timers);
>  
>  static void schedule_next_timer(struct k_itimer *timr)
>  {
> +	unsigned int overruns;
>  	struct hrtimer *timer = &timr->it.real.timer;
>  
>  	if (timr->it.real.interval.tv64 == 0)
>  		return;
>  
> -	timr->it_overrun += (unsigned int) hrtimer_forward(timer,
> -						timer->base->get_time(),
> -						timr->it.real.interval);
> +	overruns = (unsigned int) hrtimer_forward(timer,
> +					timer->base->get_time(),
> +					timr->it.real.interval);

Why not:

  posix_timer_forward(struct hrtimer *hrt, struct k_itimer *tmr)      			     
			     
and doing the forward there as well? The now optimization in
common_timer_get is not that important and if we really want to keep
it, we can hand in a pointer and read the time in the function if the
pointer is NULL.

Thanks,

	tglx
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