From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH V3 2/6] sched: idle: cpuidle: Check the latency req before idle Date: Mon, 10 Nov 2014 23:21:19 +0100 Message-ID: <54613A5F.7060107@linaro.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20141110194820.GD10501@worktop.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra 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 List-Id: linux-pm@vger.kernel.org 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 bes= t, >>> given the power usage this state should really never be eligible un= less >>> we're QoS forced or whatnot. >> >> The governors just don't use the poll state at all, except for a cou= ple of >> cases in menu.c defined above in the previous email. What is the rat= ional of >> adding a state in the cpuidle driver and do everything we can to avo= id using >> it ? From my POV, the poll state is a special state, we should remov= e 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 dif= ferent >> 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=20 optimization in menu.c (and I am still not convinced it is worth to hav= e=20 it). I don't see the point to add a state we don't want to use. 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 lo= op > 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=20 the drivers ? What about "safe_halt()" ? (arch_cpu_idle() for x86). It is also an idl= e=20 state. Why not add it in the idle state table also ? > If the arch drivers have a 'better' latency_req=3D=3D0 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 ha= ve > an (arch) interface into the idle routines, we don't need yet another= =2E --=20 Linaro.org =E2=94=82 Open source software fo= r ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog