On Fri, 10 Jun 2016 17:57:17 +0200 Sebastian Andrzej Siewior <bige...@linutronix.de> wrote:
> * Steven Rostedt | 2016-06-04 07:11:31 [-0400]: > > >From: Steven Rostedt <srost...@redhat.com> > >Date: Tue, 5 Jan 2016 14:53:09 -0500 > >Subject: [PATCH] softirq: Perform softirqs in local_bh_enable() for a limited > > amount of time > > > >To prevent starvation of tasks like ksoftirqd, if the task that is > >processing its softirqs takes more than 2 jiffies to do so, and the > >softirqs are constantly being re-added, then defer the processing to > >ksoftirqd. > > I'm not sure about this. Alison didn't scream "yes it solves my problem" > and I am not sure what it is. > It is true that in RT we don't have such a limit like in !RT. You would > need to use __raise_softirq_irqoff_ksoft() instead the normal or + > wakeup() since you may have timers pending and those need to go to the > "other" ksoftirqd. > But then I don't see much change. ksoftirqd runs now at SCHED_OTHER so > it will end up on the CPU right away unless there other tasks that need > the CPU. So the scheduler will balance it the same way. The only change > will be that softirqs which are processed in context of any application > for more than two jiffies will be moved to ksoftirqd. This could be a > win. We actually triggered a starvation due to this. I was just seeing if Alison hit the same issue we did in our tests. -- Steve
