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

    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
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