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

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Message-ID: <alpine.DEB.2.21.1908280110380.1939@nanos.tec.linutronix.de>
Date:   Wed, 28 Aug 2019 01:12:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ming Lei <ming.lei@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Long Li <longli@...rosoft.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>,
        linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

On Wed, 28 Aug 2019, Ming Lei wrote:
> On Tue, Aug 27, 2019 at 06:19:00PM +0200, Thomas Gleixner wrote:
> > > We definitely are not going to have a 64bit multiplication and division on
> > > every interrupt. Asided of that this breaks 32bit builds all over the place.
> > 
> > That said, we already have infrastructure for something like this in the
> > core interrupt code which is optimized to be lightweight in the fast path.
> > 
> > kernel/irq/timings.c
> 
> irq/timings.c is much more complicated, especially it applies EWMA to
> compute each irq's average interval. However, we only need it for
> do_IRQ() to cover all interrupt & softirq handler.

That does not justify yet another ad hoc thingy.

> Also CONFIG_IRQ_TIMINGS is usually disabled on distributions.

That's not an argument at all.

Thanks,

	tglx