Re: Interrupt Bottom Half Scheduling

[Frank Rowand <frank.rowand@gmail.com>]

On Mon, Feb 14, 2011 at 2:31 PM, Peter LaDow <petela@gocougs.wsu.edu> 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?

Is the hrtimer softirq executing when the priority 99 thread is spinning
in it's for loop?  Your "jitter Due to Large Number of Timers" email
said that the lower priority tasks don't seem to be interrupting the
priority 99 thread.

The hardware timer interupts will interrupt the priority 99 thread.  The
cost of these interrupts and the resultant calls to try_to_wake_up()
of the hrtimer softirq might be quite large considering the rate of
timer expires you mentioned in your first email.

Out of curiosity, is the system UP or SMP?

-Frank
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