linux-kernel - Re: [PATCH 00/37] softirq: Per vector masking v3

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Date:   Thu, 28 Feb 2019 09:33:15 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 00/37] softirq: Per vector masking v3

On Thu, Feb 28, 2019 at 9:12 AM Frederic Weisbecker <frederic@...nel.org> wrote:
>
> So this set should hopefully address all reviews from the v2, and
> fix all reports from the extremely useful (as always) Kbuild testing
> bot. It also completes support for all archs.

The one thing I'd still like to see is some actual performance
(latency?) numbers.

Maybe they were hiding somewhere in the pile and my quick scan missed
them. But the main argument for this was that we've had the occasional
latency issues with softirqs blocking (eg the USB v4l frame dropping
etc), and I did that SOFTIRQ_NOW_MASK because it helped one particular
case.

And you don't seem to have removed that hack, and I'd really like to
see that that thing isn't needed any more.

Because otherwise the whole series seems a bit pointless, don't you
think? If it doesn't fix that fundamental issue, then what's the point
of all this churn..

See commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous"),
which also has a couple of people listed who could hopefully re-test
the v4l latency thing with whatever USB capture dongle it was that
showed the issue.

                 Linus