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

Daniel Lezcano
2019-09-04T17:31:55Z

Hi,

On 04/09/2019 19:07, Bart Van Assche wrote:
> 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.

Was this overhead reported somewhere ?

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

From my POV, this framework could be interesting to detect this situation.

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