* Andrew Morton <[EMAIL PROTECTED]> wrote:
> > > x86: disable preemption in delay_tsc()
> > >
> > > Marin Mitov points out that delay_tsc() can misbehave if it is
> > > preempted and rescheduled on a different CPU which has a skewed
> > > TSC. Fix it by disabling preemption.
> > >
> >
> > this worries me.. this appears to effectively disable preemption
> > during udelay() and mdelay() loops... which are very obvious latency
> > inducers.
> >
> > Now you can argue that if you're preemptible you should have used
> > msleep() and co, and I'll totally buy that.
> >
> >
> > Maybe we should just check if we're still on the same cpu or
> > something, or have a cheap way to pin a process to a cpu.... but
> > both are longer term solutions.
>
> Yes, we can do better.
>
> But this bug can cause very rare failures in probably a large number
> of device drivers on a minorty of machines. Ugly. So I felt it best
> to plug it fast while people think about more sophisticated fixes.
how about using usleep() transparently if high-res timers are active and
we have !preempt_count()? That would be a sufficient solution and would
avoid all the calibration and per-cpu-ness problems.
Ingo
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