From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753874AbaEDWXF (ORCPT ); Sun, 4 May 2014 18:23:05 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:51533 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752462AbaEDWXC (ORCPT ); Sun, 4 May 2014 18:23:02 -0400 From: "Rafael J. Wysocki" To: Daniel Lezcano Cc: Linux PM list , Linux Kernel Mailing List , Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH 2/2] cpuidle / menu: Return error code if there are no suitable states Date: Mon, 05 May 2014 00:39:38 +0200 Message-ID: <4202990.UXkavWrN4U@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.14.0-rc7+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <53639B7B.2040209@linaro.org> References: <2471963.urOyfY8mOG@vostro.rjw.lan> <1684440.TX1lbQesgE@vostro.rjw.lan> <53639B7B.2040209@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, May 02, 2014 03:19:55 PM Daniel Lezcano wrote: > On 05/02/2014 02:20 PM, Rafael J. Wysocki wrote: > > On Friday, May 02, 2014 10:47:48 AM Daniel Lezcano wrote: > >> On 04/30/2014 01:16 AM, Rafael J. Wysocki wrote: > >>> On Tuesday, April 29, 2014 01:28:03 AM Rafael J. Wysocki wrote: > >>>> On Monday, April 28, 2014 01:14:32 PM Daniel Lezcano wrote: > >>>>> On 04/27/2014 02:55 PM, Rafael J. Wysocki wrote: > >> > >> [ ... ] > >> > >>> --- > >>> From: Rafael J. Wysocki > >>> Subject: cpuidle / menu: Return (-1) if there are no suitable states > >>> > >>> If there is a PM QoS latency limit and all of the sufficiently shallow > >>> C-states are disabled, the cpuidle menu governor returns 0 which on > >>> some systems is CPUIDLE_DRIVER_STATE_START and shouldn't be returned > >>> if that C-state has been disabled. > >>> > >>> Fix the issue by modifying the menu governor to return (-1) in such > >>> situations. > >>> > >>> Signed-off-by: Rafael J. Wysocki > >>> --- > >>> drivers/cpuidle/governors/menu.c | 2 +- > >>> include/linux/cpuidle.h | 2 ++ > >>> 2 files changed, 3 insertions(+), 1 deletion(-) > >>> > >>> Index: linux-pm/drivers/cpuidle/governors/menu.c > >>> =================================================================== > >>> --- linux-pm.orig/drivers/cpuidle/governors/menu.c > >>> +++ linux-pm/drivers/cpuidle/governors/menu.c > >>> @@ -296,7 +296,7 @@ static int menu_select(struct cpuidle_dr > >>> data->needs_update = 0; > >>> } > >>> > >>> - data->last_state_idx = 0; > >>> + data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1; > >> > >> In case of x86, CPUIDLE_DRIVER_STATE_START will be 1, so the select > >> function could return 0 even this one is disabled and this is not what > >> you want to happen, no ? > > > > OK, so that's a choice. We can choose to do the above or to return an error > > code if the 0 state is disabled too. The above is arguably simpler and > > matches the idea that 0 is a "fallback" state on x86. > > > > Of course, it also is confusing, because user space *can* set "disable" for > > the 0 state on x86, but that actually has no effect today AFAICS. > > Yes, the poll state is very rarely selected. > > Regarding the description of this patch, I think it would make sense to > move the duplicate pm qos checks to the cpuidle_idle_call function > directly and pass the latency req to the select function, so the zero > latency check could be done by the caller before entering select. I would prefer to have them in cpuidle_select() for various reasons (one of them being to avoid the need to pass latency_req from cpuidle_idle_call() to cpuidle_select() which isn't necessary). > > I'm mostly worried about systems where CPUIDLE_DRIVER_STATE_START is 0 > > and where menu_select() explicitly checks "disabled" and then it returns > > 0 anyway if it cannot find any other suitable state. > > For the ARM platform, the state0 and the default idle function are the > same, so disabling this state will result in calling the same idle function. > > > In my opinion that needs to be made consistent, but I don't care too much about > > which way as long as the change is not too intrusive. > > I think we can live with this patch until we remove the > CPUIDLE_DRIVER_STATE_START macro. It was introduced to factor out a > couple of drivers and now it results in a confusing-hard-to-fix-code. OK Thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.