On Fri, 4 Feb 2022 21:12:59 +0100 Sebastian Andrzej Siewior wrote: > Disabling interrupts and in the RPS case locking input_pkt_queue is > split into local_irq_disable() and optional spin_lock(). > > This breaks on PREEMPT_RT because the spinlock_t typed lock can not be > acquired with disabled interrupts. > The sections in which the lock is acquired is usually short in a sense that it > is not causing long und unbounded latiencies. One exception is the > skb_flow_limit() invocation which may invoke a BPF program (and may > require sleeping locks). > > By moving local_irq_disable() + spin_lock() into rps_lock(), we can keep > interrupts disabled on !PREEMPT_RT and enabled on PREEMPT_RT kernels. > Without RPS on a PREEMPT_RT kernel, the needed synchronisation happens > as part of local_bh_disable() on the local CPU. > ____napi_schedule() is only invoked if sd is from the local CPU. Replace > it with __napi_schedule_irqoff() which already disables interrupts on > PREEMPT_RT as needed. Move this call to rps_ipi_queued() and rename the > function to napi_schedule_rps as suggested by Jakub. > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Reviewed-by: Jakub Kicinski <kuba@xxxxxxxxxx>
