Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752555AbdGMOtA (ORCPT ); Thu, 13 Jul 2017 10:49:00 -0400 Received: from mga01.intel.com ([192.55.52.88]:12260 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752378AbdGMOs7 (ORCPT ); Thu, 13 Jul 2017 10:48:59 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,354,1496127600"; d="scan'208";a="1194996339" Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods To: Peter Zijlstra , Andi Kleen Cc: 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, paulmck@linux.vnet.ibm.com, yang.zhang.wz@gmail.com, x86@kernel.org, linux-kernel@vger.kernel.org References: <20170710144609.GD31832@tassilo.jf.intel.com> <20170710164206.5aon5kelbisxqyxq@hirez.programming.kicks-ass.net> <20170710172705.GA3441@tassilo.jf.intel.com> <20170711094157.5xcwkloxnjehieqv@hirez.programming.kicks-ass.net> <20170711160926.GA18805@lerouge> <20170711163422.etydkhhtgfthpfi5@hirez.programming.kicks-ass.net> <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> From: "Li, Aubrey" Message-ID: <16e12e23-6b28-f174-7c4b-4d719225cd3b@linux.intel.com> Date: Thu, 13 Jul 2017 22:48:55 +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: <20170713083649.febfflfl5hafkko5@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: 1067 Lines: 28 On 2017/7/13 16:36, Peter Zijlstra wrote: > On Wed, Jul 12, 2017 at 02:32:40PM -0700, Andi Kleen wrote: > >>> It uses the normal idle path, it just makes the NOHZ enter fail. >> >> Which is only a small part of the problem. > > Given the data so far provided it was by far the biggest problem. If you > want more things changed, you really have to give more data. > I have a data between arch_cpu_idle_enter and arch_cpu_idle_exit, this already excluded HW sleep. - totally from arch_cpu_idle_enter entry to arch_cpu_idle_exit return costs 9122ns - 15318ns. ---- In this period(arch idle), rcu_idle_enter costs 1985ns - 2262ns, rcu_idle_exit costs 1813ns - 3507ns Besides RCU, the period includes c-state selection on X86, a few timestamp updates and a few computations in menu governor. Also, deep HW-cstate latency can be up to 100+ microseconds, even if the system is very busy, CPU still has chance to enter deep cstate, which I guess some outburst workloads are not happy with it. That's my major concern without a fast idle path. Thanks, -Aubrey