Re: [PATCH net-next 1/4] net: dev: Remove the preempt_disable() in netif_rx_internal().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-02-03 13:00:06 [+0100], Toke Høiland-Jørgensen wrote:
> > Here is the code in larger context:
> >
> > #ifdef CONFIG_RPS
> >     if (static_branch_unlikely(&rps_needed)) {
> >         struct rps_dev_flow voidflow, *rflow = &voidflow;
> >         int cpu;
> >
> >         preempt_disable();
> >         rcu_read_lock();
> >
> >         cpu = get_rps_cpu(skb->dev, skb, &rflow);
> >         if (cpu < 0)
> >             cpu = smp_processor_id();
> >
> >         ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
> >
> >         rcu_read_unlock();
> >         preempt_enable();
> >     } else
> > #endif
> >
> > This code needs the preempt_disable().
> 
> This is mostly so that the CPU ID stays the same throughout that section
> of code, though, right? So wouldn't it work to replace the
> preempt_disable() with a migrate_disable()? That should keep _RT happy,
> no?

It would but as mentioned previously: BH is disabled and
smp_processor_id() is stable.

> -Toke

Sebastian