On 10/05/22 14:01, Hillf Danton wrote: > On 4 Oct 2022 18:13:52 -0700 John Stultz <jstultz@xxxxxxxxxx> > > On Tue, Oct 4, 2022 at 5:22 PM Hillf Danton <hdanton@xxxxxxxx> wrote: > > > On 3 Oct 2022 19:29:36 -0700 John Stultz <jstultz@xxxxxxxxxx> > > > > > > > > Why would ksoftirqd preempt the rt task? > > > > > > > For example the kthread becomes sensitive to latency. > > > > Is it the case where > > the ksoftirqd thread is configured to run at higher rtprio? > > > Yes, you are right. I don't see a problem here. If a sys-admin configures their ksoftirqds to be a higher priority RT tasks than the audio threads, then they better know what they're doing :-) The issue at hand here is that the softirqs boundedness is hard to control. And the scheduling delays ensued are hard to deal with by any sys-admin. Networking has actually introduced some knobs to help control that - but the tricky bit of still being able to deliver high throughput networking while keeping the softirq bounded to minimize scheduling delays/latencies. I think even for PREEMPT_RT, high performance networking could be impacted to achieve the required low latency. See this paper which explores this duality: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.702.7571&rep=rep1&type=pdf With WiFi 6 and 5G mobile networks, phones are actually expected to deliver multi-gigabit network throughputs. Cheers -- Qais Yousef
