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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1515734588.10188.36.camel@gmx.de>
Date:   Fri, 12 Jan 2018 06:23:08 +0100
From:   Mike Galbraith <efault@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Dmitry Safonov <dima@...sta.com>,
        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 12:22 -0800, Linus Torvalds wrote:
> On Thu, Jan 11, 2018 at 12:16 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > Note that when I implemented TCP Small queues, I did experiments between
> > using a work queue or a tasklet, and workqueues added unacceptable P99
> > latencies, when many user threads are competing with kernel threads.
> 
> Yes.
> 
> So I think one solution might be to have a hybrid system, where we do
> the softirq's synchronously normally (which is what you really want
> for good latency).
> 
> But then fall down on a threaded model - but that fallback case should
> be per-softirq, not global. So if one softirq uses a lot of CPU time,
> that shouldn't affect the latency of other softirqs.
> 
> So maybe we could get rid of the per-cpu ksoftirqd entirely, and
> replace it with with per-cpu and per-softirq workqueues?

How would that be better than what RT used to do, and I still do for my
RT kernels via boot option, namely split ksoftirqd into per-softirq
threads.

	-Mike