Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

Keith Busch
2019-09-06T14:28:03Z

On Fri, Sep 06, 2019 at 09:48:21AM +0800, Ming Lei wrote:
> When one IRQ flood happens on one CPU:
>
> 1) softirq handling on this CPU can't make progress
>
> 2) kernel thread bound to this CPU can't make progress
>
> For example, network may require softirq to xmit packets, or another irq
> thread for handling keyboards/mice or whatever, or rcu_sched may depend
> on that CPU for making progress, then the irq flood stalls the whole
> system.
>
> >
> > AFAIU, there are fast medium where the responses to requests are faster
> > than the time to process them, right?
>
> Usually medium may not be faster than CPU, now we are talking about
> interrupts, which can be originated from lots of devices concurrently,
> for example, in Long Li'test, there are 8 NVMe drives involved.

Why are all 8 nvmes sharing the same CPU for interrupt handling?
Shouldn't matrix_find_best_cpu_managed() handle selecting the least used
CPU from the cpumask for the effective interrupt handling?