Re: [PATCH] ia64: disable preemption in udelay()

[Bill Davidsen]

Lee Revell wrote:
> On Thu, 2005-12-15 at 18:12 -0800, John Hawkes wrote:
>
> > From: "Lee Revell" <rlrevell@xxxxxxxxxxx>
> >
> > > 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.
> >
> > What about 100usec non-preemptible sections?
>
>
> That will disappear into the noise, in normal usage these happen all the
> time.  500usec non preemptible regions are rare (~1 hour to show up) and
> 1ms very rare (24 hours).  My tests show that 300 usec or so is a good
> place to draw the line if you don't want it to show up in latency tests.

I may be misreading the original post, but the problem is described as 
one where the TSC is not syncronised and a CPU switch takes place. Would 
the correct solution be to somehow set CPU affinity temporarily in such 
a way as to avoid disabling preempt at all?

The preempt doesn't seem to be the root problem, so it's unlikely to be 
the best solution...

--
   -bill davidsen (davidsen@xxxxxxx)
"The secret to procrastination is to put things off until the
 last possible moment - but no longer"  -me
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