linux-kernel - Re: [RFC PATCH 0/4] softirq: Per vector threading v3

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Message-ID: <1516702432.2554.37.camel@redhat.com>
Date:   Tue, 23 Jan 2018 11:13:52 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Levin Alexander <alexander.levin@...izon.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Dmitry Safonov <dima@...sta.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Radu Rendec <rrendec@...sta.com>,
        Ingo Molnar <mingo@...nel.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3

Hi,

On Fri, 2018-01-19 at 16:46 +0100, Frederic Weisbecker wrote:
> As per Linus suggestion, this take doesn't limit the number of occurences
> per jiffy anymore but instead defers a vector to workqueues as soon as
> it gets re-enqueued on IRQ tail.
> 
> No tunable here, so testing should be easier.
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	softirq/thread-v3
> 
> HEAD: 6835e92cbd70ef4a056987d2e1ed383b294429d4

I tested this series in the UDP flood scenario, binding the user space
process receiving the packets on the same CPU processing the related
IRQ, and the tput sinks nearly to 0, like before Eric's patch.

The perf tool says that almost all the softirq processing is done
inside the workqueue, but the user space process is scheduled very
rarely, while before this series, in this scenario, ksoftirqd and the
user space process got a fair share of the CPU time.

Cheers,

Paolo