Messages in this thread Patch in this message | | | Subject | [PATCH/RFC] msleep() with hrtimers | From | Jonathan Corbet <> | Date | Sun, 15 Jul 2007 16:42:44 -0600 |
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The OLPC folks and I recently discovered something interesting: on a HZ=100 system, a call to msleep(1) will delay for about 20ms. The combination of jiffies timekeeping and rounding up means that the minimum delay from msleep will be two jiffies, never less. That led to multi-second delays in a driver which does a bunch of short msleep() calls and, in response, a change to mdelay(), which will come back in something closer to the requested time.
Here's another approach: a reimplementation of msleep() and msleep_interruptible() using hrtimers. On a system without real hrtimers this code will at least drop down to single-jiffy delays much of the time (though not deterministically so). On my x86_64 system with Thomas's hrtimer/dyntick patch applied, msleep(1) gives almost exactly what was asked for.
jon
Use hrtimers for msleep() and msleep_interruptible()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
--- 2.6.22-vanilla/kernel/timer.c 2007-07-15 13:08:36.000000000 -0600 +++ 2.6.22-timer/kernel/timer.c 2007-07-15 16:13:34.000000000 -0600 @@ -1522,18 +1522,43 @@ unregister_time_interpolator(struct time } #endif /* CONFIG_TIME_INTERPOLATION */ + + + +static void do_msleep(unsigned int msecs, struct hrtimer_sleeper *sleeper, + int sigs) +{ + enum hrtimer_mode mode = HRTIMER_MODE_REL; + int state = sigs ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE; + + /* + * This is really just a reworked and simplified version + * of do_nanosleep(). + */ + hrtimer_init(&sleeper->timer, CLOCK_MONOTONIC, mode); + sleeper->timer.expires = ktime_set(0, msecs*NSEC_PER_MSEC); + hrtimer_init_sleeper(sleeper, current); + + do { + set_current_state(state); + hrtimer_start(&sleeper->timer, sleeper->timer.expires, mode); + if (sleeper->task) + schedule(); + hrtimer_cancel(&sleeper->timer); + mode = HRTIMER_MODE_ABS; + } while (sleeper->task && !(sigs && signal_pending(current))); +} + /** * msleep - sleep safely even with waitqueue interruptions * @msecs: Time in milliseconds to sleep for */ void msleep(unsigned int msecs) { - unsigned long timeout = msecs_to_jiffies(msecs) + 1; + struct hrtimer_sleeper sleeper; - while (timeout) - timeout = schedule_timeout_uninterruptible(timeout); + do_msleep(msecs, &sleeper, 0); } - EXPORT_SYMBOL(msleep); /** @@ -1542,11 +1567,15 @@ EXPORT_SYMBOL(msleep); */ unsigned long msleep_interruptible(unsigned int msecs) { - unsigned long timeout = msecs_to_jiffies(msecs) + 1; + struct hrtimer_sleeper sleeper; + ktime_t left; - while (timeout && !signal_pending(current)) - timeout = schedule_timeout_interruptible(timeout); - return jiffies_to_msecs(timeout); -} + do_msleep(msecs, &sleeper, 1); + if (! sleeper.task) + return 0; + left = ktime_sub(sleeper.timer.expires, + sleeper.timer.base->get_time()); + return max(((long) ktime_to_ns(left))/NSEC_PER_MSEC, 1L); +} EXPORT_SYMBOL(msleep_interruptible); - 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/
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