Re: [RT] rt priority losing

From: Thomas Gleixner
Date: Mon Jul 24 2006 - 12:42:44 EST

At Mon, 24 Jul 2006 12:37:22 -0400,
Steven Rostedt wrote:
> > > So this can be a problem, if the softirq function holds a lock of a high
> > > priority task, and is running boosted. If another timer goes off with a
> > > lower priority, we can lower the priority of the softirqd and lose the
> > > inherited priority that it was running at.
> >
> > There is a check for that inside setscheduler():
> > p->prio = rt_mutex_getprio(p);
> OK, you are right about this. The PI chain should not be affected. But
> this could still be a problem if the softirq was running at a high prio
> for a task when a lower prio callback needs to be made. It looks like
> timer is removed from the base before the function runs. So when the
> interrupt looks at the base to determine the priority to set it at, it
> might actually lower the priority of a running hrtimer thread.

The correct solution is to run the callback in the context of
the thread which will receive it and get rid of the softirq.

I experimented with this already, but its more than a saturday
afternoon project.

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