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([2a01:e34:ed2f:f020:8499:4f69:106b:da0]) by smtp.googlemail.com with ESMTPSA id 18sm5593307wmj.21.2021.03.09.11.03.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Mar 2021 11:03:52 -0800 (PST) Subject: Re: [PATCH 5/5] powercap/drivers/dtpm: Scale the power with the load To: Lukasz Luba Cc: rafael@kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org References: <20210301212149.22877-1-daniel.lezcano@linaro.org> <20210301212149.22877-5-daniel.lezcano@linaro.org> From: Daniel Lezcano Message-ID: Date: Tue, 9 Mar 2021 20:03:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Lukasz, thanks for your comments, one question below. On 09/03/2021 11:01, Lukasz Luba wrote: [ ... ] >>   +static u64 scale_pd_power_uw(struct cpumask *cpus, u64 power) > > renamed 'cpus' into 'pd_mask', see below > >> +{ >> +    unsigned long max, util; >> +    int cpu, load = 0; > > IMHO 'int load' looks odd when used with 'util' and 'max'. > I would put in the line above to have them all the same type and > renamed to 'sum_util'. > >> + >> +    for_each_cpu(cpu, cpus) { > > I would avoid the temporary CPU mask in the get_pd_power_uw() > with this modified loop: > > for_each_cpu_and(cpu, pd_mask, cpu_online_mask) { > > >> +        max = arch_scale_cpu_capacity(cpu); >> +        util = sched_cpu_util(cpu, max); >> +        load += ((util * 100) / max); > > Below you can find 3 optimizations. Since we are not in the hot > path here, it's up to if you would like to use all/some of them > or just ignore. > > 1st optimization. > If we use 'load += (util << 10) / max' in the loop, then > we could avoid div by 100 and use a right shift: > (power * load) >> 10 > > 2nd optimization. > Since we use EM CPU mask, which span all CPUs with the same > arch_scale_cpu_capacity(), you can avoid N divs inside the loop > and do it once, below the loop. > > 3rd optimization. > If we just simply add all 'util' into 'sum_util' (no mul or div in > the loop), then we might just have simple macro > > #define CALC_POWER_USAGE(power, sum_util, max) \ >     (((power * (sum_util << 10)) / max) >> 10) I don't understand the 'max' division, I was expecting here something like: ((sum_util << 10) / sum_max) >> 10) no ? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog