linux-kernel - Re: [RFC PATCH 2/3] softirq: implement interrupt flood detection

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Message-ID: <20191218122922.GR2871@hirez.programming.kicks-ass.net>
Date:   Wed, 18 Dec 2019 13:29:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Long Li <longli@...rosoft.com>, Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [RFC PATCH 2/3] softirq: implement interrupt flood detection

On Wed, Dec 18, 2019 at 11:49:41AM +0100, Peter Zijlstra wrote:
> 
> _If_ you want to do something like this, do it like the below. That only
> adds a few instruction to irq_exit() and only touches a cacheline that's
> already touched.
> 
> It computes both the avg duration and the avg inter-arrival-time of
> hardirqs. Things get critical when:
> 
> 	inter-arrival-avg < 2*duration-avg
> 
> or something like that.

Better yet, try something like:

bool cpu_irq_heavy(int cpu)
{
	return cpu_util_irq(cpu_rq(cpu)) >= arch_scale_cpu_capacity(cpu);
}