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

Bart Van Assche
2019-09-04T17:07:52Z

On 9/3/19 12:50 AM, Daniel Lezcano wrote:
> On 03/09/2019 09:28, Ming Lei wrote:
>> On Tue, Sep 03, 2019 at 08:40:35AM +0200, Daniel Lezcano wrote:
>>> It is a scheduler problem then ?
>>
>> Scheduler can do nothing if the CPU is taken completely by handling
>> interrupt & softirq, so seems not a scheduler problem, IMO.
>
> Why? If there is a irq pressure on one CPU reducing its capacity, the
> scheduler will balance the tasks on another CPU, no?

Only if CONFIG_IRQ_TIME_ACCOUNTING has been enabled. However, I don't
know any Linux distro that enables that option. That's probably because
that option introduces two rdtsc() calls in each interrupt. Given the
overhead introduced by this option, I don't think this is the solution
Ming is looking for.

See also irqtime_account_irq() in kernel/sched/cputime.c.

Bart.