From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753194AbdEDPD3 (ORCPT ); Thu, 4 May 2017 11:03:29 -0400 Received: from mail.kernel.org ([198.145.29.136]:58596 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753995AbdEDPCA (ORCPT ); Thu, 4 May 2017 11:02:00 -0400 Date: Thu, 4 May 2017 11:01:55 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: LKML , Thomas Gleixner , Ingo Molnar , Clark Williams , Daniel Bristot de Oliveira , John Kacur , Scott Wood Subject: Re: [PATCH tip/sched/core v2] sched/rt: Simplify the IPI rt balancing logic Message-ID: <20170504110155.2ed7b158@gandalf.local.home> In-Reply-To: <20170504144128.k2a5vxebtyly7qlv@hirez.programming.kicks-ass.net> References: <20170424114732.1aac6dc4@gandalf.local.home> <20170504144128.k2a5vxebtyly7qlv@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 4 May 2017 16:41:28 +0200 Peter Zijlstra wrote: > On Mon, Apr 24, 2017 at 11:47:32AM -0400, Steven Rostedt wrote: > > + /* Keep the loop going if the IPI is currently active */ > > + atomic_inc_return(&rq->rd->rto_loop_next); > > What's the return for? -ENOCONTEXT (too much cut from email) /me goes and finds his email that he sent. /* Keep the loop going if the IPI is currently active */ atomic_inc_return(&rq->rd->rto_loop_next); /* Only one CPU can initiate a loop at a time */ if (!rto_start_trylock(&rq->rd->rto_loop_start)) return; Ah, it's not needed. I think I had that to supply a full memory barrier for a previous version, but now that rto_start_trylock() is: static inline bool rto_start_trylock(atomic_t *v) { return !atomic_cmpxchg(v, 0, 1); } Which supplies its own memory barrier, it can now be a simple atomic_inc(). Thanks, will update. -- Steve