Received-SPF: pass (google.com: domain of linux-kernel+bounces-186528-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Date: Wed, 22 May 2024 09:57:58 -0700
From: Bjorn Andersson <quic_bjorande@quicinc.com>
To: Shivnandan Kumar <quic_kshivnan@quicinc.com>
CC: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Bjorn Andersson
	<andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <quic_rgottimu@quicinc.com>
Subject: Re: [PATCH] soc: qcom: icc-bwmon: Update zone1_thres_count to 3
Message-ID: <Zk4kFoM4wN5/BJuw@hu-bjorande-lv.qualcomm.com>
References: <20240522081508.1488592-1-quic_kshivnan@quicinc.com>
 <bc973b4f-fe8b-44e5-afbc-f3ce8a6fc873@linaro.org>
 <baa55c1f-2670-4a3c-abcf-ea4e841e4a1e@quicinc.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <baa55c1f-2670-4a3c-abcf-ea4e841e4a1e@quicinc.com>

On Wed, May 22, 2024 at 02:35:21PM +0530, Shivnandan Kumar wrote:
> 
> 
> On 5/22/2024 1:58 PM, Krzysztof Kozlowski wrote:
> > On 22/05/2024 10:15, Shivnandan Kumar wrote:
> > > Update zone1_thres_count to 3 from 16 so that
> > > driver can reduce bus vote in 3 sample windows instead
> > > of waiting for 16 windows. This is in line with downstream
> > > implementation.
> > > 
> > 
> > This might make bwmon quite jittery. I don't think downstream is the
> > source of truth here. Please provide some measurements *on mainline tree*.
> > 
> 
> Hi Krzysztof,
> 
> The 16-window (64 ms) waiting time is too long to reduce the bus vote.
> At higher FPS, there will be multiple frames in 64ms e.g. 4 frames at 60FPS
> in 64ms. Hence, delay of 64ms in decision making will lead to higher power
> regression. I’ve tested this change for 4K video playback on mainline tree,
> and there’s a significant power-saving.
> 

As requested by Krzysztof already, update your commit message to capture
such motivation.

Please read and follow this:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes

> I propose to make it a tunable,so that user space can tune it
> based on runtime depending on fps.
> 

I presume that in e.g. Android there could be some sort of power HAL
that tweaks this value dynamically? In a general purpose system, how do
we make sure that this value stays relevant for multiple types of use
cases?

> USECASE                     zone1_thres_count=16     zone1_thres_count=3
> 4K video playback           236.15 mA	             203.15 mA

4k video playback is a fairly specific (and generally unusual) use case.
Is there any impact (negative or positive) for other use
cases/workloads?

Regards,
Bjorn

> 
> Thanks,
> Shivnandan
> 
> > Best regards,
> > Krzysztof
> >