From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756867Ab3JHKWB (ORCPT ); Tue, 8 Oct 2013 06:22:01 -0400 Received: from merlin.infradead.org ([205.233.59.134]:32789 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756219Ab3JHKVz (ORCPT ); Tue, 8 Oct 2013 06:21:55 -0400 Date: Tue, 8 Oct 2013 12:21:42 +0200 From: Peter Zijlstra To: Ingo Molnar Cc: Christoph Lameter , Tejun Heo , akpm@linuxfoundation.org, Eric Dumazet , netdev@vger.kernel.org, Steven Rostedt , linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [raw v1 2/4] [NET] Use raw_cpu ops for SNMP stats Message-ID: <20131008102142.GT3081@twins.programming.kicks-ass.net> References: <20131007183226.334180014@linux.com> <0000014194309205-d0af4d2d-a046-4189-b4f0-ffea37374988-000000@email.amazonses.com> <20131008072114.GA4455@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131008072114.GA4455@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 08, 2013 at 09:21:14AM +0200, Ingo Molnar wrote: > > * Christoph Lameter wrote: > > > SNMP stats are not protected by preemption but by bh handling. > > Most forms of bh exclusion work via the preemption count though, and > softirq contexts themselves are generally not preemptible [to other CPUs] > either. > > So the warnings should, in most cases, not trigger. Right, so softirqs run either in the irq tail at which point preempt_count += SOFTIRQ_OFFSET and thus preemption is disabled, or it runs in ksoftirqd which has strict cpu affinity which also disables the warning, and it also increments preempt_count with SOFTIRQ_OFFSET to exclude the softirq from interrupts while its running, also disabling the warning. So it should very much not trigger.. if it does you want to know about it.