Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751436AbdGQOC5 (ORCPT ); Mon, 17 Jul 2017 10:02:57 -0400 Received: from mga09.intel.com ([134.134.136.24]:37827 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751332AbdGQOCy (ORCPT ); Mon, 17 Jul 2017 10:02:54 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,374,1496127600"; d="scan'208";a="126040862" Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods To: Peter Zijlstra Cc: paulmck@linux.vnet.ibm.com, Andi Kleen , Frederic Weisbecker , Christoph Lameter , Aubrey Li , tglx@linutronix.de, len.brown@intel.com, rjw@rjwysocki.net, tim.c.chen@linux.intel.com, arjan@linux.intel.com, yang.zhang.wz@gmail.com, x86@kernel.org, linux-kernel@vger.kernel.org References: <496d4921-5768-cd1e-654b-38630b7d2e13@linux.intel.com> <20170712083410.ualmvnvzoohyami5@hirez.programming.kicks-ass.net> <20170712213240.GE3441@tassilo.jf.intel.com> <20170713083649.febfflfl5hafkko5@hirez.programming.kicks-ass.net> <16e12e23-6b28-f174-7c4b-4d719225cd3b@linux.intel.com> <20170713145311.z4zxlyd2dospeoqg@hirez.programming.kicks-ass.net> <20170713152032.GM2393@linux.vnet.ibm.com> <58a312d3-bd3d-9427-109b-5d81a5fd7c76@linux.intel.com> <20170714040553.GR2393@linux.vnet.ibm.com> <20170717135851.tpo6si6my6vcpwla@hirez.programming.kicks-ass.net> From: "Li, Aubrey" Message-ID: Date: Mon, 17 Jul 2017 22:02:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170717135851.tpo6si6my6vcpwla@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1247 Lines: 30 On 2017/7/17 21:58, Peter Zijlstra wrote: > On Mon, Jul 17, 2017 at 09:24:51PM +0800, Li, Aubrey wrote: >> On 2017/7/14 12:05, Paul E. McKenney wrote: >>> >>> More specifically: rcu_needs_cpu(), rcu_prepare_for_idle(), >>> rcu_cleanup_after_idle(), rcu_eqs_enter(), rcu_eqs_enter_common(), >>> rcu_dynticks_eqs_enter(), do_nocb_deferred_wakeup(), >>> rcu_dynticks_task_enter(), rcu_eqs_exit(), rcu_eqs_exit_common(), >>> rcu_dynticks_task_exit(), rcu_dynticks_eqs_exit(). >>> >>> The first three (rcu_needs_cpu(), rcu_prepare_for_idle(), and >>> rcu_cleanup_after_idle()) should not be significant unless you have >>> CONFIG_RCU_FAST_NO_HZ=y. If you do, it would be interesting to learn >>> how often invoke_rcu_core() is invoked from rcu_prepare_for_idle() >>> and rcu_cleanup_after_idle(), as this can raise softirq. Also >>> rcu_accelerate_cbs() and rcu_try_advance_all_cbs(). >>> >>> Knowing which of these is causing the most trouble might help me >>> reduce the overhead in the current idle path. >> >> I measured two cases, nothing notable found. > > So skipping rcu_idle_{enter,exit}() is not in fact needed at all? > I think it would make more sense if we still put them under the case where tick is really stopped. Thanks, -Aubrey