Re: Interrupt Bottom Half Scheduling

[Peter LaDow <petela@gocougs.wsu.edu>]

Note sure how that is possible.  This is related to my earlier posting
about timing jitter.  Our code is basically this:

while(1)
{
  t1 = clock_gettime()
  for(i=0; i < 10000; i++)
  t2 = clock_gettime()

  diff = t2 - 1
}

This task is pending on nothing.  Unless clock_gettime() causes some
sort of priority inversion, I don't see the problem.  We see
significant jitter on the for-loop when there are a significant number
of other kernel timers.  Now, as we understand it, the hrtimers run in
the softirq.  But if the softirq is priority 50, and this for-loop is
priority 99, it shouldn't be affected by the softirq thread.

Pete

On Mon, Feb 14, 2011 at 3:04 PM, Sven-Thorsten Dietrich
<thebigcorporation@gmail.com> wrote:
> On Mon, 2011-02-14 at 14:31 -0800, Peter LaDow wrote:
>> How is the scheduling of the hrtimers softirq thread handled?
>>
>> When querying the RT priority of the hrtimer softirq, I get a priority
>> of 50.  But when running a priority 99 thread, we still seem to be
>> getting interrupted.  Shouldn't the hrtimer softirq be put off until
>> the CPU is idle or a lower priority task is running?
>
> Does your prio 99 thread perhaps encounter a prio inversion dependency
> on one of the softriq threads?
>
>>
>> Thanks,
>> Pete
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