From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753213AbeCFCPP (ORCPT ); Mon, 5 Mar 2018 21:15:15 -0500 Received: from mga09.intel.com ([134.134.136.24]:51700 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752507AbeCFCPO (ORCPT ); Mon, 5 Mar 2018 21:15:14 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,429,1515484800"; d="scan'208";a="205773500" Subject: Re: [RFC/RFT][PATCH 4/7] cpuidle: menu: Split idle duration prediction from state selection To: Peter Zijlstra , "Rafael J. Wysocki" Cc: "Rafael J. Wysocki" , Thomas Gleixner , Frederic Weisbecker , Paul McKenney , Thomas Ilsche , Doug Smythies , Rik van Riel , Mike Galbraith , LKML , Linux PM References: <1657351.s4RTvEoqBQ@aspire.rjw.lan> <2332986.m9oRvTSu8E@aspire.rjw.lan> <20180305113803.GO25201@hirez.programming.kicks-ass.net> <20180305125012.GA25181@hirez.programming.kicks-ass.net> <20180305135322.GV25201@hirez.programming.kicks-ass.net> From: "Li, Aubrey" Message-ID: <43825f88-762e-11e5-d70a-45152b95599d@linux.intel.com> Date: Tue, 6 Mar 2018 10:15:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <20180305135322.GV25201@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 On 2018/3/5 21:53, Peter Zijlstra wrote: > On Mon, Mar 05, 2018 at 02:05:10PM +0100, Rafael J. Wysocki wrote: >> On Mon, Mar 5, 2018 at 1:50 PM, Peter Zijlstra wrote: >>> On Mon, Mar 05, 2018 at 12:47:23PM +0100, Rafael J. Wysocki wrote: > >>>> IOW, the target residency of the selected state doesn't tell you how >>>> much time you should expect to be idle in general. >>> >>> Right, but I think that measure isn't of primary relevance. What we want >>> to know is: 'should I stop the tick' and 'what C state do I go to'. I understood the benefit of mapping duration to state number, is duration <-> state number mapping a generic solution to all arches? Back to the user's concern is, "I'm running a latency sensitive application, and I want idle switching ASAP". So I think the user may not care about what C state to go into, that is, even if a deeper state has chance to go, the user striving for a higher workload score may still not want it? >>> >>> In order to answer those questions we need durations as input, but I >>> don't think we should preserve durations throughout. The scheme from the >>> above link reduces to N states in order to deal with arbitrary >>> distributions, only the actual states -- ie boundaries where our answers >>> changes -- are relevant, anything inside those boundaries would lead to >>> the exact same answer anyway. >> >> I generally agree here, but I'm not convinced about flagging the >> states, splitting them and so on. > > I think linking them like that makes sense, but I can see room for > discussion... > >> Maybe just return a "nohz" indicator from cpuidle_select() in addition >> to the state index and make the decision in the governor? > > Much better option than returning a duration :-) > So what does "nohz = disable and state index = deepest" mean? This combination does not make sense for performance only purpose? Thanks, -Aubrey