Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754880AbbDOMup (ORCPT ); Wed, 15 Apr 2015 08:50:45 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:36179 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754823AbbDOMud (ORCPT ); Wed, 15 Apr 2015 08:50:33 -0400 Message-ID: <552E5E99.6060901@linaro.org> Date: Wed, 15 Apr 2015 14:50:33 +0200 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Peter Zijlstra CC: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, nicolas.pitre@linaro.org Subject: Re: [PATCH 1/3] cpuidle: Store the idle start time stamp References: <1429092024-20498-1-git-send-email-daniel.lezcano@linaro.org> <20150415102057.GR5029@twins.programming.kicks-ass.net> <552E5992.2050404@linaro.org> <20150415124246.GW5029@twins.programming.kicks-ass.net> In-Reply-To: <20150415124246.GW5029@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1667 Lines: 45 On 04/15/2015 02:42 PM, Peter Zijlstra wrote: > On Wed, Apr 15, 2015 at 02:29:06PM +0200, Daniel Lezcano wrote: >> On 04/15/2015 12:20 PM, Peter Zijlstra wrote: >>> On Wed, Apr 15, 2015 at 12:00:22PM +0200, Daniel Lezcano wrote: >>>> + target_state->idle_stamp = ktime_to_us(ktime_get()); >>> >>> ktime_get_ns(); >>> >> >> Hmm, sounds like I missed we are dealing with different units (us / ns) in >> cpuidle / sched. >> >> Would it make sense to store the time into a ktime structure instead and use >> the relevant function depending on the place we are inspecting the value >> from ? > > Why would you ever want to use us? Does ARM enjoy calculating /1000? > > Ah, I see the !scalar ktime got whacked, good! At which point the u64 ns > and ktime are the same. That said I prefer the u64 over ktime because > its easier to manipulate. Ok. I was trying to save one variable on the stack by reusing the idle_stamp value but if we store it in a different unit, then we have to keep it in order to have usecond for the governors. I was thinking about converting to nanosecond the cpuidle framework but it is not worth to do that as the resolution is too high for the idle states. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/