linux-kernel - Re: [PATCH] arm64: dts: qcom: x1e80100: Add performance hint for boost clock

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Message-ID: <270a2b73-087e-466d-9ba9-fb696167d507@jia.je>
Date: Fri, 25 Oct 2024 16:08:54 +0800
From: Jiajie Chen <c@....je>
To: Marc Zyngier <maz@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: x1e80100: Add performance hint for
 boost clock


On 2024/10/25 15:58, Marc Zyngier wrote:
> On Fri, 25 Oct 2024 04:12:58 +0100,
> Jiajie Chen <c@....je> wrote:
>> The x1e80100 CPU can have up to two cores running at 4.0 GHz, with one
>> core in the second cluster (cores 4-7) and the other in the third
>> cluster (cores 8-11). However, the scheduler is currently unaware of
>> this, leading to scenarios where a single core benchmark might run at
>> 3.4 GHz when scheduled to the first cluster.
>>
>> This patch introduces capacity-dmips-mhz nodes to each CPU node in the
>> DTS. For cores numbered 4 and 8, the capacities are set to 1200, while
>> others are set to 1024. This ensures that the two cores can be
>> prioritized for scheduling. The value 1200 is derived from approximately
>> `1024/3.4*4.0`.
>>
>> Note that capacity-dmips-mhz is not ideally suited for this purpose, as
>> it was designed to differentiate between performance and efficient
>> cores, not for core boosting. According to its definition, DMIPS/MHz
>> actually decreases with higher frequencies. However, since the CPU does
>> not support AMU, and no elegant solution was found, this approach is
>> used as a workaround.
> Are you sure?
>
> [    0.570323] CPU features: detected: Activity Monitors Unit (AMU) on CPU0-11
>
> So activity monitors are available. Not that what you have here is not
> useful, but this comment seems a bit... surprising.

Sorry for the false claim, I was looking for AMU at /proc/cpuinfo, which 
is not there. But it did not help the scheduling somehow. Let me have a 
look at it.


Best regards,

Jiajie Chen

>
> Thanks,
>
> 	M.
>