From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752722AbaKKKVE (ORCPT ); Tue, 11 Nov 2014 05:21:04 -0500 Received: from casper.infradead.org ([85.118.1.10]:36183 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752041AbaKKKVB (ORCPT ); Tue, 11 Nov 2014 05:21:01 -0500 Date: Tue, 11 Nov 2014 11:20:58 +0100 From: Peter Zijlstra To: Daniel Lezcano Cc: rjw@rjwysocki.net, preeti@linux.vnet.ibm.com, nicolas.pitre@linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, patches@linaro.org, lenb@kernel.org Subject: Re: [PATCH V3 2/6] sched: idle: cpuidle: Check the latency req before idle Message-ID: <20141111102058.GI10501@worktop.programming.kicks-ass.net> References: <1415370687-18688-1-git-send-email-daniel.lezcano@linaro.org> <1415370687-18688-3-git-send-email-daniel.lezcano@linaro.org> <20141110124111.GN3337@twins.programming.kicks-ass.net> <5460D5EF.2000805@linaro.org> <20141110152803.GX10501@worktop.programming.kicks-ass.net> <5460E0A5.9040508@linaro.org> <20141110161530.GB10501@worktop.programming.kicks-ass.net> <5460F386.1050109@linaro.org> <20141110194820.GD10501@worktop.programming.kicks-ass.net> <54613A5F.7060107@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54613A5F.7060107@linaro.org> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 10, 2014 at 11:21:19PM +0100, Daniel Lezcano wrote: > On 11/10/2014 08:48 PM, Peter Zijlstra wrote: > >On Mon, Nov 10, 2014 at 06:19:02PM +0100, Daniel Lezcano wrote: > >>>I really don't get why the governors should know about this though, its > >>>just another state, they should iterate all states and pick the best, > >>>given the power usage this state should really never be eligible unless > >>>we're QoS forced or whatnot. > >> > >>The governors just don't use the poll state at all, except for a couple of > >>cases in menu.c defined above in the previous email. What is the rational of > >>adding a state in the cpuidle driver and do everything we can to avoid using > >>it ? From my POV, the poll state is a special state, we should remove from > >>the driver's idle states like the arch_cpu_idle() is a specific idle state > >>only used in idle.c (but which may overlap with an idle state in different > >>archs eg. cpu_do_idle() and the 0th idle state). > > > >So I disagree, I think poll-idle is an idle mode just like all the > >others. It should be an available state to the governor and it should > >treat it like any other. > > The governors are just ignoring it, except for a small timer optimization in > menu.c (and I am still not convinced it is worth to have it). I don't see > the point to add a state we don't want to use. The ignoring it is _wrong_. Make that go away and you'll get rid of most of the STATE_START crap. The governors are the place where we combine the QoS constraints with idle predictors and pick an idle state, polling is a valid state to pick, and given QoS constraints it might be the only state to pick. > Eg. on my server it was called 2 times over 1313856 times. > > >I don't tihnk the whole ARCH_HAS_CPU_RELAX thing makes any kind of > >sense, _every_ arch has some definition of it, the generic polling loop > >is always a valid idle implementation. > > > >What we can do is always populate the idle state table with it before > >calling the regular drivers. > > I am not sure to understand. You want to add the poll idle loop in all the > drivers ? > > What about "safe_halt()" ? (arch_cpu_idle() for x86). It is also an idle > state. Why not add it in the idle state table also ? Because the latter is actually arch specific, whereas the idle polling thing is not. You can _always_ poll idle, its generic, its valid, and its guaranteed the most responsive method. The arch drivers get to add arch specific idle states; if a x86 cpuidle driver wants to add hlt they can.