From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758262AbbA0PE5 (ORCPT ); Tue, 27 Jan 2015 10:04:57 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:51079 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752487AbbA0PEz (ORCPT ); Tue, 27 Jan 2015 10:04:55 -0500 Date: Tue, 27 Jan 2015 16:04:46 +0100 From: Peter Zijlstra To: Xunlei Pang Cc: linux-kernel@vger.kernel.org, Juri Lelli Subject: Re: [PATCH 2/5] sched/deadline: Remove cpu_active_mask from cpudl_find() Message-ID: <20150127150446.GF21418@twins.programming.kicks-ass.net> References: <1421642980-10045-1-git-send-email-pang.xunlei@linaro.org> <1421642980-10045-2-git-send-email-pang.xunlei@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1421642980-10045-2-git-send-email-pang.xunlei@linaro.org> 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 Mon, Jan 19, 2015 at 04:49:37AM +0000, Xunlei Pang wrote: > cpu_active_mask is rarely changeable, so remove this operation > to gain a little performance. > > If there is a change in cpu_active_mask, rq_online_dl() and > rq_offline_dl() should take care of it normally, so cpudl:: > free_cpus carries enough information for us. > > For the rare case(causing a task put onto a dying cpu) which > rq_offline_dl() can't handle timely, then it can be handled > through _cpu_down()->...->multi_cpu_stop()->migration_call() > ->migrate_tasks(), preventing the task from hanging on the > dead cpu. Maybe; I'll need to go crawl through the long and twisted history of active_mask here :/