From: Andy Whitcroft <apw@canonical.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Patrick Pannuto <ppannuto@codeaurora.org>,
Jonathan Corbet <corbet@lwn.net>,
Israel Schlesinger <israels@codeaurora.org>,
linux-kernel@vger.kernel.org, joe@perches.com,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] checkpatch: Add warnings for use of mdelay()
Date: Wed, 28 Jul 2010 10:44:14 +0100 [thread overview]
Message-ID: <20100728094414.GA3586@shadowen.org> (raw)
In-Reply-To: <20100727121610.64b38cfa.akpm@linux-foundation.org>
On Tue, Jul 27, 2010 at 12:16:10PM -0700, Andrew Morton wrote:
> On Tue, 27 Jul 2010 10:32:54 -0700
> Patrick Pannuto <ppannuto@codeaurora.org> wrote:
>
> > On 07/27/2010 10:31 AM, Jonathan Corbet wrote:
> > > On Tue, 27 Jul 2010 10:11:11 -0700
> > > Israel Schlesinger <israels@codeaurora.org> wrote:
> > >
> > >> mdelay is a busy-wait loop which is wasteful. If at all possible,
> > >> callers should use msleep instead of mdelay.
> > >>
> > >> The only time mdelay is really appropriate is in atomic context,
> > >> however, delays of 1ms+ in atomic context are rather expensive, so
> > >> a warning for this case is probably appropriate as well to encourage
> > >> people to move such expensive delays outside of atomic context
> > >
> > > Once upon a time, msleep(1) would sleep for 20ms, while mdelay(1) gave
> > > a 1ms delay. My patch to fix msleep() at that time didn't get in due
> > > to concerns about the cost of using hrtimers. Perhaps msleep() has
> > > gotten better, but, if not, actually getting a 1ms delay remains a
> > > valid reason for using mdelay() instead IMO. It made a difference of a
> > > few seconds at open time for a driver I was doing at the time.
> > >
> > > jon
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > > Please read the FAQ at http://www.tux.org/lkml/
> >
> > Check out the recently added usleep in -tip, and the checkpatch patch
> > pending in my queue that fixes that case (I'll send in a few hours ;) )
> >
>
> The message should point people at usleep_range(), I'd suggest. It's a
> more power-friendly way of sleeping.
>
> That assumes that the below patch gets merged - the people who handle
> timer-related things are presently, err, asleep.
>
>
> From: Patrick Pannuto <ppannuto@codeaurora.org>
>
> usleep[_range] are finer precision implementations of msleep and are
> designed to be drop-in replacements for udelay where a precise sleep /
> busy-wait is unnecessary. They also allow an easy interface to specify
> slack when a precise (ish) wakeup is unnecessary to help minimize wakeups
>
> Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
> Acked-by: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> include/linux/delay.h | 6 ++++++
> kernel/timer.c | 22 ++++++++++++++++++++++
> 2 files changed, 28 insertions(+)
>
> diff -puN include/linux/delay.h~timers-add-usleep-timer include/linux/delay.h
> --- a/include/linux/delay.h~timers-add-usleep-timer
> +++ a/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);
> +}
>
> static inline void ssleep(unsigned int seconds)
> {
> diff -puN kernel/timer.c~timers-add-usleep-timer kernel/timer.c
> --- a/kernel/timer.c~timers-add-usleep-timer
> +++ a/kernel/timer.c
> @@ -1763,3 +1763,25 @@ unsigned long msleep_interruptible(unsig
> }
>
> 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;
If this interface is taking a min and max in micro-seconds, then does
not the delta need also to be converted to nano-seconds?
schedule_hrtimeout_range seems to call hrtimer_set_expires_range_ns
which seems to generally be called with 'delta_ns'. Something like:
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);
-apw
next prev parent reply other threads:[~2010-07-28 9:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-27 17:11 [PATCH] checkpatch: Add warnings for use of mdelay() Israel Schlesinger
2010-07-27 17:22 ` Joe Perches
2010-07-27 17:31 ` Jonathan Corbet
2010-07-27 17:32 ` Patrick Pannuto
2010-07-27 19:16 ` Andrew Morton
2010-07-28 9:44 ` Andy Whitcroft [this message]
2018-07-04 18:18 Prakruthi Deepak Heragu
2018-07-04 18:30 ` Joe Perches
2018-07-05 8:19 ` Dan Carpenter
2018-07-06 5:49 ` Julia Lawall
2018-07-07 12:09 ` Jia-Ju Bai
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