Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.20.1801172251280.2326@nanos>
References: <1515782670.7007.3.camel@gmx.de> <20180117.153049.1803664333084879932.davem@davemloft.net>
 <CA+55aFwOv1SBOz6+0GxLxbK5riei83AQRJEHUTXUehSWfBq=Fg@mail.gmail.com>
 <20180117.164932.1269304606476934540.davem@davemloft.net> <alpine.DEB.2.20.1801172251280.2326@nanos>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 17 Jan 2018 13:58:10 -0800
Message-ID: <CA+55aFzk0Lh1kQRRvOQKrjMfkcuQem0aV5D9cCUmmtfw7ZamkQ@mail.gmail.com>
Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     David Miller <davem@davemloft.net>, Mike Galbraith <efault@gmx.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Eric Dumazet <edumazet@google.com>,
        Dmitry Safonov <dima@arista.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        Ingo Molnar <mingo@kernel.org>,
        Sasha Levin <alexander.levin@verizon.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Radu Rendec <rrendec@arista.com>,
        Rik van Riel <riel@redhat.com>,
        Stanislaw Gruszka <sgruszka@redhat.com>,
        Wanpeng Li <wanpeng.li@hotmail.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jan 17, 2018 at 1:54 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> raise_softirq() -> raise_softirq_irqoff()
>
>         set_softirq_bit();
>
>         if (!in_interrupt())
>                 wake_softirqd();
>
> So if the caller is not in hard or soft interrupt context, which includes
> bottom half disabled regions softirqd is woken.

That does seem unnecessarily expensive, and maybe we could just do it
with thread flag (TIF_NOTIFY_RESUME or whatever).

In fact, that was what I *thought* we did. Maybe I just remember some
historical behavior.

Since networking seems to largely prefer softirqd anyway, maybe that
wake_softirqd() is the right thing to do anyway.

             Linus