From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1167182AbdDXIwQ (ORCPT ); Mon, 24 Apr 2017 04:52:16 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:52037 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1166882AbdDXIwH (ORCPT ); Mon, 24 Apr 2017 04:52:07 -0400 Date: Mon, 24 Apr 2017 10:51:54 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: LKML , Thomas Gleixner , Ingo Molnar , Clark Williams , Daniel Bristot de Oliveira , John Kacur Subject: Re: [RFC][PATCH tip/sched/core] sched/rt: Simplify the IPI rt balancing logic Message-ID: <20170424085154.d6ny6vmbmuaoxiln@hirez.programming.kicks-ass.net> References: <20170421224929.1a4bbeec@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170421224929.1a4bbeec@gandalf.local.home> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 21, 2017 at 10:49:29PM -0400, Steven Rostedt wrote: > When a CPU schedules in a lower priority task and wants to make sure > overloaded CPUs know about it. It increments the rto_loop_next. Then it does > an atomic_inc_return() on rto_loop_start. If the returned value is not "1", > then it does atomic_dec() on rt_loop_start and returns. If the value is "1", > then it will take the rto_lock to synchronize with a possible IPI being sent > around to the overloaded CPUs. > + start = atomic_inc_return(&rq->rd->rto_loop_start); > + if (start != 1) > + goto out; > +out: > + atomic_dec(&rq->rd->rto_loop_start); Did you just write a very expensive test-and-set trylock?