linux-kernel - Re: [RFC PATCH 0/5] softirq: Per vector threading v2

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Message-ID: <1516279448.2762.7.camel@arista.com>
Date:   Thu, 18 Jan 2018 12:44:08 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Frederic Weisbecker <frederic@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Mauro Carvalho Chehab <mchehab@...pensource.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Levin Alexander <alexander.levin@...izon.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Radu Rendec <rrendec@...sta.com>,
        Ingo Molnar <mingo@...nel.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH 0/5] softirq: Per vector threading v2

On Thu, 2018-01-18 at 05:09 +0100, Frederic Weisbecker wrote:
> On Wed, Jan 17, 2018 at 07:09:39PM -0800, Linus Torvalds wrote:
> > It should never trigger under any normal load, but I think it
> > *should*
> > trigger under the load that the networking people worry about. If
> > you
> > get a flood of UDP packets, and spend a lot of time in softirqs,
> > I'm
> > pretty sure you'd hit that case of seeing the same softirq re-
> > raised
> > fairly naturally and quickly.
> 
> Ok after a quick tracing check, it seems that executing the same
> softirq
> vector twice in the same interrupt does not happen without much
> stress.

Uhm, yes it should.. but that was what I originally saw on hw - that
raising a new softirq under UDP packet storm might happen slower than
expected. And a new softirq is raised only after the first one was
processed. Which results in rare deferring.

-- 
            Dima