On Thu, 18 Jan 2024 09:27:54 +0100 Sebastian Andrzej Siewior wrote: > On 2024-01-17 18:04:47 [-0800], Jakub Kicinski wrote: > > Oh, and I'm bringing it up here, because CONFIG_RT can throw > > in "need_resched()" into the napi_rx_has_budget(), obviously. > > need_resched() does not work on PREEMPT_RT the way you think. This > context (the NAPI poll callback) is preemptible and (by default) runs at > SCHED_FIFO 50 (within a threaded IRQ) so a context switch can happen at > any time by a task with higher priority. > If threadA gets preempted and owns a lock that threadB, with higher > priority, wants then threadA will get back on CPU, inherit the priority > of the threadB and continue to run until it releases the lock. > > If this is the per-CPU BH lock (which I want to remove) then it will > continue until all softirqs complete. So there's no way for a process to know on RT that someone with higher prio is waiting for it to release its locks? :(
