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

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Message-ID: <20180111164311.GM3040@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Jan 2018 17:43:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Miller <davem@...emloft.net>
Cc:     edumazet@...gle.com, dima@...sta.com, frederic@...nel.org,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        0x7f454c46@...il.com, akpm@...ux-foundation.org,
        fweisbec@...il.com, hannes@...essinduktion.org, mingo@...nel.org,
        alexander.levin@...izon.com, pabeni@...hat.com,
        paulmck@...ux.vnet.ibm.com, rrendec@...sta.com, riel@...hat.com,
        sgruszka@...hat.com, tglx@...utronix.de, wanpeng.li@...mail.com
Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd
 context

On Thu, Jan 11, 2018 at 11:38:40AM -0500, David Miller wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Thu, 11 Jan 2018 17:32:04 +0100
> 
> > You just introduced a 2ms preempt-disable region I think, that's not
> > cool for PREEMPT and a plain bug on PREEMPT_RT.
> 
> I'd just like to know what the difference is between ksoftirqd running
> softirq work for 2ms and the real softirq context doing it.  The
> latter already has this "2ms preempt-disable region" of sorts, right?

True I suppose.. and PREEMPT_RT does the whole softirq business
differently anyway.

I'll go back to staring at PTI crud..