On Thu, Apr 18, 2024 at 11:02:06AM +0200, Jesper Dangaard Brouer wrote: > > > On 18/04/2024 04.19, Yosry Ahmed wrote: [...] > > > > I will keep the high-level conversation about using the mutex here in > > the cover letter thread, but I am wondering why we are keeping the > > lock dropping logic here with the mutex? > > > > I agree that yielding the mutex in the loop makes less sense. > Especially since the raw_spin_unlock_irqrestore(cpu_lock, flags) call > will be a preemption point for my softirq. But I kept it because, we > are running a CONFIG_PREEMPT_VOLUNTARY kernel, so I still worried that > there was no sched point for other userspace processes while holding the > mutex, but I don't fully know the sched implication when holding a mutex. > Are the softirqs you are interested in, raised from the same cpu or remote cpu? What about local_softirq_pending() check in addition to need_resched() and spin_needbreak() checks? If softirq can only be raised on local cpu then convert the spin_lock to non-irq one (Please correct me if I am wrong but on return from hard irq and not within bh or irq disabled spin_lock, the kernel will run the pending softirqs, right?). Did you get the chance to test these two changes or something similar in your prod environment?
