Re: [PATCH/RFC] msleep() with hrtimers

Ingo Molnar
2007-07-16T10:49:19Z

* Jonathan Corbet <corbet@lwn.net> wrote:

> 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>

i certainly like this - an msleep() is like mdelay(), so there are real
delays (and not timeouts) involved, so converting to hrtimers is the
right thing to do from a conceptual POV too.

Acked-by: Ingo Molnar <mingo@elte.hu>

Ingo