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

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Message-ID: <dbnc6kq2heyva2c4c4bt6kwo62sifi4kws6nup7etnnyyzawes@uag66bceq6is>
Date: Fri, 25 Oct 2024 14:04:41 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jiajie Chen <c@....je>
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 Fri, Oct 25, 2024 at 11:12:58AM +0800, Jiajie Chen 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.
> 
> With this patch, we observe two cores running at full 4.0 GHz without
> core binding. The single core score of Geekbench 6 increases from 2452
> to 2892, both without core binding. Tested on Surface Laptop 7.

I think this is a nice hack, but I'd prefer to see scheduler being
improved instead. From my (ignorant) point of view this should be close
to SMT-based scheduling. We should split the jobs between the clusters,
if that provides better power utilisation.

> 
> Signed-off-by: Jiajie Chen <c@....je>
> ---
>  arch/arm64/boot/dts/qcom/x1e80100.dtsi | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 

-- 
With best wishes
Dmitry