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([2a01:e34:ed2f:f020:1d1:2aa9:b538:861]) by smtp.googlemail.com with ESMTPSA id v4sm85202897wmg.22.2019.08.05.00.37.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Aug 2019 00:37:44 -0700 (PDT) Subject: Re: [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver To: Martin Kepplinger , viresh.kumar@linaro.org, kevin.wangtao@linaro.org, leo.yan@linaro.org, edubezval@gmail.com, vincent.guittot@linaro.org, javi.merino@kernel.org, rui.zhang@intel.com, daniel.thompson@linaro.org Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <1522945005-7165-7-git-send-email-daniel.lezcano@linaro.org> <20190805051111.24318-1-martin.kepplinger@puri.sm> From: Daniel Lezcano Openpgp: preference=signencrypt Autocrypt: addr=daniel.lezcano@linaro.org; prefer-encrypt=mutual; keydata= mQINBFv/yykBEADDdW8RZu7iZILSf3zxq5y8YdaeyZjI/MaqgnvG/c3WjFaunoTMspeusiFE sXvtg3ehTOoyD0oFjKkHaia1Zpa1m/gnNdT/WvTveLfGA1gH+yGes2Sr53Ht8hWYZFYMZc8V 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qePOXubgouxumi5RQs1+crBmCDa/AyJHKdG2mqCt9fx5EPbDpw6Zzx7hgURh4ikHoS7/tLjK iqWjuat8/HWc01yEd8rtkGuUcMqbCi1XhcAmkaOnX8FYscMRoyyMrWClRZEQRokqZIj79+PR adkDXtr4MeL8BaB7Ij2oyRVjXUwhFQNKi5Z5Rve0a3zvGkkqw8Mz20BOksjSWjAF6g9byukl CUVjC03PdMSufNLK06x5hPc/c4tFR4J9cLrV+XxdCX7r0zGos9SzTPGNuIk1LK++S3EJhLFj 4eoWtNhMWc1uiTf9ENza0ntqH9XBWEQ6IA1gubCniGG+Xg== Message-ID: <2d7f1caa-351a-8fdc-bb6b-151f7313a042@linaro.org> Date: Mon, 5 Aug 2019 09:37:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190805051111.24318-1-martin.kepplinger@puri.sm> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 05/08/2019 07:11, Martin Kepplinger wrote: > --- [ ... ] >> +static s64 cpuidle_cooling_runtime(struct cpuidle_cooling_device *idle_cdev) >> +{ >> + s64 next_wakeup; >> + unsigned long state = idle_cdev->state; >> + >> + /* >> + * The function should not be called when there is no >> + * mitigation because: >> + * - that does not make sense >> + * - we end up with a division by zero >> + */ >> + if (!state) >> + return 0; >> + >> + next_wakeup = (s64)((idle_cdev->idle_cycle * 100) / state) - >> + idle_cdev->idle_cycle; >> + >> + return next_wakeup * NSEC_PER_USEC; >> +} >> + > > There is a bug in your calculation formula here when "state" becomes 100. > You return 0 for the injection rate, which is the same as "rate" being 0, > which is dangerous. You stop cooling when it's most necessary :) Right, thanks for spotting this. > I'm not sure how much sense really being 100% idle makes, so I, when testing > this, just say if (state == 100) { state = 99 }. Anyways, just don't return 0. > > Daniel, thanks a lot for these additions! Could you send an update of this? Yes, I'm working on a new version. > btw, that's what I'm referring to: > https://lore.kernel.org/linux-pm/1522945005-7165-1-git-send-email-daniel.lezcano@linaro.org/ > I know it's a little old already, but it seems like there hasn't been any > equivalent solution in the meantime, has it? > > Using cpuidle for cooling is way more effective than cpufreq (which often > hardly is). On which platform that happens? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog