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

[Ingo Molnar <mingo@elte.hu>]

* 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