linux-kernel - Re: [RFC PATCH 1/4] softirq: Limit vector to a single iteration on IRQ tail

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Date:   Sun, 21 Jan 2018 17:30:09 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     David Miller <davem@...emloft.net>
Cc:     torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        alexander.levin@...izon.com, peterz@...radead.org,
        mchehab@...pensource.com, hannes@...essinduktion.org,
        paulmck@...ux.vnet.ibm.com, wanpeng.li@...mail.com,
        dima@...sta.com, tglx@...utronix.de, akpm@...ux-foundation.org,
        pabeni@...hat.com, rrendec@...sta.com, mingo@...nel.org,
        sgruszka@...hat.com, riel@...hat.com, edumazet@...gle.com
Subject: Re: [RFC PATCH 1/4] softirq: Limit vector to a single iteration on
 IRQ tail

On Fri, Jan 19, 2018 at 01:47:27PM -0500, David Miller wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Fri, 19 Jan 2018 10:25:03 -0800
> 
> > On Fri, Jan 19, 2018 at 8:16 AM, David Miller <davem@...emloft.net> wrote:
> >>
> >> So this "get requeued" condition I think will trigger always for
> >> networking tunnel decapsulation.
> > 
> > Hmm. Interesting and a perhaps bit discouraging.
> > 
> > Will it always be just a _single_ level of indirection, or will double
> > tunnels (I assume some people do that, just because the universe is
> > out to get us) then result in this perhaps repeating several times?
> 
> Every level of tunnel encapsulation will trigger a new softirq.
> 
> So if you have an IP tunnel inside of an IP tunnel that will trigger
> twice.

So we may likely need to come back to a call counter based limit :-s