On Thu, 2005-12-15 at 17:52 -0800, Zwane Mwaikambo wrote:
> On Thu, 15 Dec 2005, Luck, Tony wrote:
>
> > On Wed, Dec 14, 2005 at 03:25:26PM -0800, [email protected] wrote:
> > > Sending this to a wider audience:
> > >
> > > The udelay() inline for ia64 uses the ITC. If CONFIG_PREEMPT is enabled
> > > and the platform has unsynchronized ITCs and the calling task migrates
> > > to another CPU while doing the udelay loop, then the effective delay may
> > > be too short or very, very long.
> > >
> > > The most simple fix is to disable preemption around the udelay looping.
> > > The downside is that this inhibits realtime preemption for cases of long
> > > udelays. One datapoint: an SGI realtime engineer reports that if
> > > CONFIG_PREEMPT is turned off, that no significant holdoffs are
> > > are attributed to udelay().
> > >
> > > I am reluctant to propose a much more complicated patch (that disables
> > > preemption only for "short" delays, and uses the global RTC as the time
> > > base for longer, preemptible delays) unless this patch introduces
> > > significant and unacceptable preemption delays.
> >
> > Stuck between a rock and the proverbial hard place.
> >
> > I think that the more complex patch is needed though. If some crazy
> > driver has a pre-emptible udelay(10000), then you really don't want
> > to spin for that long without allowing preemption.
>
> If it's a preemptible sleep period it should just use msleep.
There are 10 drivers that udelay(10000) or more and a TON that
udelay(1000). Turning those all into 1ms+ non preemptible sections will
be very bad.
Lee
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