From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH V3 2/6] sched: idle: cpuidle: Check the latency req before idle Date: Mon, 10 Nov 2014 20:48:20 +0100 Message-ID: <20141110194820.GD10501@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from bombadil.infradead.org ([198.137.202.9]:41860 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751410AbaKJTs0 (ORCPT ); Mon, 10 Nov 2014 14:48:26 -0500 Content-Disposition: inline In-Reply-To: <5460F386.1050109@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org 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 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. 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. If the arch drivers have a 'better' latency_req==0 idle routine -- note my argument on the ppc issue, I think its wrong -- it can replace the existing one. We should further remove all the special casing in the governors, its always a valid state, but it should hardly ever be the most desirable state. I think the whole arch specific idle loop is a mistake, we already have an (arch) interface into the idle routines, we don't need yet another.