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

From: Bill Davidsen <davidsen_at_tmr.com>
Date: 2005-12-23 08:45:08
Lee Revell wrote:
> On Thu, 2005-12-15 at 18:12 -0800, John Hawkes wrote:
> 
>>From: "Lee Revell" <rlrevell@joe-job.com>
>>
>>>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@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me
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Received on Fri Dec 23 08:46:10 2005

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