Re: 2.6.15-rt3 + Open Posix Test Suite

On Tue, 2006-01-10 at 15:03 -0800, Daniel Walker wrote:
> It's worth noting that a few tests in the current Open Posix Test Suite
> hang RT systems.
>
> Specifically this test (hope this url comes through),
>
> http://cvs.sourceforge.net/viewcvs.py/*checkout*/posixtest/posixtestsuite/conformance/interfaces/sched_setparam/10-1.c?rev=1.2
>
> sched_setparam test 10-1.c and I think 9-1.c .
>
> The 10-1 test spawns some children at SCHED_FIFO priority 99 , then runs
> the following,
>
> void child_process(){
> alarm(2);
>
> while(1) {
> (*shmptr)++;
> sched_yield();
> }
> }
>
> I'm sure this is what's hanging the system, the yield() is one issue.
> Another is why the alarm() is never delivered .

This runs a while loop at SCHED_FIFO prio 99? And alarm never happens.
Doesn't the alarm get activated by the softirqd that is running at a
lower priority? Seems that this is starving out the softirq from
getting the alarm.

I believe that Thomas once had priorities attached to the timers. I'd
like to see that again, and may even start adding them myself, such that
when a process activates a timer, when that timer goes off, the softirq
will get the priority of the timer. But this has some complications to
be sorted out.

-- Steve


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