linux-kernel - Re: [PATCH 1/4] timer: Added usleep[

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Date:	Wed, 28 Jul 2010 13:23:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Patrick Pannuto <ppannuto@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, apw@...onical.com, corbet@....net,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH 1/4] timer: Added usleep[_range] timer

On Wed, 28 Jul 2010 12:33:04 -0700
Patrick Pannuto <ppannuto@...eaurora.org> wrote:

> diff --git a/include/linux/delay.h b/include/linux/delay.h
> index fd832c6..2538c95 100644
> --- a/include/linux/delay.h
> +++ b/include/linux/delay.h
> @@ -45,6 +45,12 @@ extern unsigned long lpj_fine;
>  void calibrate_delay(void);
>  void msleep(unsigned int msecs);
>  unsigned long msleep_interruptible(unsigned int msecs);
> +void usleep_range(unsigned long min, unsigned long max);
> +
> +static inline void usleep(unsigned long usecs)
> +{
> +	usleep_range(usecs, usecs * 2);
> +}
>  
>  static inline void ssleep(unsigned int seconds)
>  {
> diff --git a/kernel/timer.c b/kernel/timer.c
> index ee305c8..c2253dd 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1750,3 +1750,25 @@ unsigned long msleep_interruptible(unsigned int msecs)
>  }
>  
>  EXPORT_SYMBOL(msleep_interruptible);
> +
> +static int __sched do_usleep_range(unsigned long min, unsigned long max)
> +{
> +	ktime_t kmin;
> +	unsigned long delta;
> +
> +	kmin = ktime_set(0, min * NSEC_PER_USEC);
> +	delta = (max - min) * NSEC_PER_USEC;
> +	return schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL);
> +}
> +
> +/**
> + * usleep_range - Drop in replacement for udelay where wakeup is flexible
> + * @min: Minimum time in usecs to sleep
> + * @max: Maximum time in usecs to sleep
> + */
> +void usleep_range(unsigned long min, unsigned long max)
> +{
> +	__set_current_state(TASK_UNINTERRUPTIBLE);
> +	do_usleep_range(min, max);
> +}
> +EXPORT_SYMBOL(usleep_range);

This is different from the patch I merged and I'm not seeing any
explanation for the change.

The implementation of usleep() looks odd.  The longer we sleep, the
greater the possible inaccuracy.  A code comment which explains the
thinking and which warns people about the implications is needed.
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