From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755342Ab3LRPMX (ORCPT ); Wed, 18 Dec 2013 10:12:23 -0500 Received: from merlin.infradead.org ([205.233.59.134]:49227 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754959Ab3LRPMW (ORCPT ); Wed, 18 Dec 2013 10:12:22 -0500 Date: Wed, 18 Dec 2013 16:11:58 +0100 From: Peter Zijlstra To: Frederic Weisbecker Cc: "Paul E. McKenney" , LKML , Thomas Gleixner , Ingo Molnar , Steven Rostedt , John Stultz , Alex Shi , Kevin Hilman Subject: Re: [PATCH 05/13] rcu: Fix unraised IPI to timekeeping CPU Message-ID: <20131218151158.GV21999@twins.programming.kicks-ass.net> References: <1387320692-28460-1-git-send-email-fweisbec@gmail.com> <1387320692-28460-6-git-send-email-fweisbec@gmail.com> <20131217232100.GC19211@linux.vnet.ibm.com> <20131218141348.GA18464@localhost.localdomain> <20131218142240.GP19211@linux.vnet.ibm.com> <20131218145610.GE18464@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131218145610.GE18464@localhost.localdomain> 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 Wed, Dec 18, 2013 at 03:56:12PM +0100, Frederic Weisbecker wrote: > Because scheduler_ipi() conditionally calls irq_enter() and irq_exit() > (I wonder if that's a good idea btw, is that here to deal with spurious > scheduler IPIs of some sort?) No its because the traditional scheduler IPI did all the work from the interrupt return path -- and like the comment in there says, for many of the IPIs that's still true. So going through the architectures and making all scheduler_ipi callers do irq_enter/exit would actually make them slower.