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

Roman Zippel
2007-07-16T14:11:44Z

Hi,

On Sun, 15 Jul 2007, Jonathan Corbet 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.

BTW there is another thing to consider. If you already run with hrtimer/
dyntick, there is not much reason to keep HZ at 100, so you could just
increase HZ to get the same effect.

bye, Roman