linux-kernel - Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context

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Date:   Thu, 11 Jan 2018 20:46:26 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Miller <davem@...emloft.net>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Radu Rendec <rrendec@...sta.com>,
        Rik van Riel <riel@...hat.com>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd
 context

On Thu, 2018-01-11 at 12:40 -0800, Linus Torvalds wrote:
> On Thu, Jan 11, 2018 at 12:34 PM, Dmitry Safonov <dima@...sta.com>
> wrote:
> > 
> > I could try to write a PoC for that..
> > What should be the trigger to fall into workqueue?
> > How to tell if there're too many softirqs of the kind?
> 
> I suspect it would have to be time-based, probably using the
> scheduler clock.

I thought about this, but I was a bit afraid of how much pricey it
would be recalculate it each clock. Well, might just try to write that
and measure the impact.

> Most softirqs are really really small. So just counting them probably
> isn't all that meaningful, although the count is good as a fallback
> (as shown by the jiffy issues).
> 
> The good news is that we only have a fairly small handful of
> softirqs,
> so counting/timing them separately is still mainly a pretty small
> array (which needs to be percpu, of course).