From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Lukasz Luba <lukasz.luba@arm.com>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Cc: amitk@kernel.org, rui.zhang@intel.com, viresh.kumar@linaro.org,
rafael@kernel.org, dietmar.eggemann@arm.com, nm@ti.com,
sboyd@kernel.org, sudeep.holla@arm.com, cristian.marussi@arm.com,
matthias.bgg@gmail.com, linux-mediatek@lists.infradead.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/4] PM: EM: convert power field to micro-Watts precision and align drivers
Date: Thu, 7 Jul 2022 10:31:09 +0200 [thread overview]
Message-ID: <9b4bd8b5-d5d9-7f75-128a-87b727ad0bd7@linaro.org> (raw)
In-Reply-To: <20220707071555.10085-2-lukasz.luba@arm.com>
On 07/07/2022 09:15, Lukasz Luba wrote:
> The milli-Watts precision causes rounding errors while calculating
> efficiency cost for each OPP. This is especially visible in the 'simple'
> Energy Model (EM), where the power for each OPP is provided from OPP
> framework. This can cause some OPPs to be marked inefficient, while
> using micro-Watts precision that might not happen.
>
> Update all EM users which access 'power' field and assume the value is
> in milli-Watts.
>
> Solve also an issue with potential overflow in calculation of energy
> estimation on 32bit machine. It's needed now since the power value
> (thus the 'cost' as well) are higher.
>
> Example calculation which shows the rounding error and impact:
>
> power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz
>
> power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000
> power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18
>
> power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961
> power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21
>
> max_freq = 2000MHz
>
> cost_a_mW = 18 * 2000MHz/500MHz = 72
> cost_a_uW = 18000 * 2000MHz/500MHz = 72000
>
> cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better
> cost_b_uW = 21961 * 2000MHz/600MHz = 73203
>
> The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly
> better that the 'cost_b_uW' (this patch uses micro-Watts) and such
> would have impact on the 'inefficient OPPs' information in the Cpufreq
> framework. This patch set removes the rounding issue.
>
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
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next prev parent reply other threads:[~2022-07-07 8:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-07 7:15 [PATCH v2 0/4] Energy Model power in micro-Watts and SCMI v3.1 alignment Lukasz Luba
2022-07-07 7:15 ` [PATCH v2 1/4] PM: EM: convert power field to micro-Watts precision and align drivers Lukasz Luba
2022-07-07 8:31 ` Daniel Lezcano [this message]
2022-07-07 10:44 ` Lukasz Luba
2022-07-07 10:53 ` Viresh Kumar
2022-07-07 10:53 ` Lukasz Luba
2022-07-07 7:15 ` [PATCH v2 2/4] Documentation: EM: Switch to micro-Watts scale Lukasz Luba
2022-07-07 7:15 ` [PATCH v2 3/4] firmware: arm_scmi: Get detailed power scale from perf Lukasz Luba
2022-07-07 7:15 ` [PATCH v2 4/4] cpufreq: scmi: Support the power scale in micro-Watts in SCMI v3.1 Lukasz Luba
2022-07-07 10:52 ` Viresh Kumar
2022-07-07 10:46 ` [PATCH v2 0/4] Energy Model power in micro-Watts and SCMI v3.1 alignment Lukasz Luba
2022-07-15 8:56 ` Lukasz Luba
2022-07-15 17:18 ` Rafael J. Wysocki
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