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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 12 Jan 2018 09:51:42 -0800
Message-ID: <CA+55aFxRF=9xav_XEMizV2vqiX6S4SigBxFTrXwWTRrTKG1Yvw@mail.gmail.com>
Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context
To: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Eric Dumazet <edumazet@google.com>,
        Dmitry Safonov <dima@arista.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Miller <davem@davemloft.net>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>,
        Paolo Abeni <pabeni@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Radu Rendec <rrendec@arista.com>,
        Rik van Riel <riel@redhat.com>,
        Stanislaw Gruszka <sgruszka@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpeng.li@hotmail.com>
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Sender: linux-kernel-owner@vger.kernel.org

On Fri, Jan 12, 2018 at 9:44 AM, Mike Galbraith <efault@gmx.de> wrote:
>
> Nah, a misunderstanding happened.  RT that still offers full threading
> creates per-softirq threads per cpu.  The regular trees split ksoftirqd
> into only two threads per cpu, one processes timer/hrtimer softriqs,
> the other processes the rest.

Ok, that sounds like it should work, but it also sounds like it's very
specific to RT itself.

For example, the dvb issue was not about the timer softirqs, but about
the tasklet ones.

So maybe we wouldn't need to split it for _every_ softirq, but we'd
need to split it more than just along the timer case.

And it does sound a bit excessive to have ten fixed threads for every
CPU. The days when tens of CPU's meant "huge system" are gone. These
days it can be a phone.

            Linus