From: Andrew Morton <akpm@linux-foundation.org>
To: Patrick Pannuto <ppannuto@codeaurora.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
Israel Schlesinger <israels@codeaurora.org>,
linux-kernel@vger.kernel.org, apw@canonical.com, joe@perches.com,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] checkpatch: Add warnings for use of mdelay()
Date: Tue, 27 Jul 2010 12:16:10 -0700 [thread overview]
Message-ID: <20100727121610.64b38cfa.akpm@linux-foundation.org> (raw)
In-Reply-To: <4C4F1846.3090103@codeaurora.org>
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;
+ 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);
_
next prev parent reply other threads:[~2010-07-27 19:17 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 [this message]
2010-07-28 9:44 ` Andy Whitcroft
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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