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

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Message-ID: <CANn89iK3M97MN0Pf3nXb+UAqqhUWOdSthHRBTYCwP75Ax_hO8Q@mail.gmail.com>
Date:   Tue, 9 Jan 2018 10:02:53 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, 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>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 Tue, Jan 9, 2018 at 5:36 AM, Dmitry Safonov <dima@...sta.com> wrote:
> Warning: Not merge-ready
>
> I. Current workflow of ksoftirqd.
>   Softirqs are processed in the context of ksoftirqd iff they are
>   being raised very frequently. How it works:
>   do_softirq() and invoke_softirq() deffer pending softirq iff
>

...

>
>   Note, that I tested in VMs and I've found that if I produce more
>   hw irqs on the host, than the results for master are not that
>   dramatically bad, but still much worse then with RFC.
>   By that reason I have qualms if my test's results are correct.

Note that deferring all NET RX/TX to ksoftirqd is going to
dramatically hurt tail latencies.

You really should test with RPC like workloads (netperf -t TCP_RR) and
hundred of threads per cpu :/

It seems we are going to revert/adapt 4cd13c21b2 , not defer more
stuff to ksoftirqd.

Thanks