Date: Thu, 11 Jan 2018 17:43:11 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Miller <davem@davemloft.net>
Cc: edumazet@google.com, dima@arista.com, frederic@kernel.org,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
        0x7f454c46@gmail.com, akpm@linux-foundation.org,
        fweisbec@gmail.com, hannes@stressinduktion.org, mingo@kernel.org,
        alexander.levin@verizon.com, pabeni@redhat.com,
        paulmck@linux.vnet.ibm.com, rrendec@arista.com, riel@redhat.com,
        sgruszka@redhat.com, tglx@linutronix.de, wanpeng.li@hotmail.com
Subject: Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd
 context
Message-ID: <20180111164311.GM3040@hirez.programming.kicks-ass.net>
References: <1515681091.3039.21.camel@arista.com>
 <CANn89i+mVmzrZ14Kttt=J0wsDOMHhm8CHiMRLQwEZXMxiVpftg@mail.gmail.com>
 <20180111163204.GE6176@hirez.programming.kicks-ass.net>
 <20180111.113840.1908989919518121712.davem@davemloft.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180111.113840.1908989919518121712.davem@davemloft.net>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org

On Thu, Jan 11, 2018 at 11:38:40AM -0500, David Miller wrote:
> From: Peter Zijlstra <peterz@infradead.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..