linux-kernel - Re: [PATCH V6 2/3] soc: qcom: boot_stat: Add Driver Support for Boot Stats

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Message-ID: <cf533b92-a03d-ed61-2811-2528a531f5fd@quicinc.com>
Date:   Thu, 11 May 2023 10:11:49 -0700
From:   Trilok Soni <quic_tsoni@...cinc.com>
To:     Bjorn Andersson <andersson@...nel.org>,
        Souradeep Chowdhury <quic_schowdhu@...cinc.com>,
        Arnd Bergmann <arnd@...db.de>
CC:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, Sibi Sankar <quic_sibis@...cinc.com>,
        Rajendra Nayak <quic_rjendra@...cinc.com>
Subject: Re: [PATCH V6 2/3] soc: qcom: boot_stat: Add Driver Support for Boot
 Stats

On 5/11/2023 10:07 AM, Bjorn Andersson wrote:
> On Tue, May 09, 2023 at 03:52:22AM -0700, Souradeep Chowdhury wrote:
>> All of Qualcomm's proprietary Android boot-loaders capture boot time
>> stats, like the time when the bootloader started execution and at what
>> point the bootloader handed over control to the kernel etc. in the IMEM
>> region. This information is captured in a specific format by this driver
>> by mapping a structure to the IMEM memory region and then accessing the
>> members of the structure to show the information within debugfs file.
>> This information is useful in verifying if the existing boot KPIs have
>> regressed or not. The information is shown in milliseconds, a sample
>> log from sm8450(waipio) device is as follows:-
>>
>> /sys/kernel/debug/qcom_boot_stats # cat abl_time
>> 17898 ms
>> /sys/kernel/debug/qcom_boot_stats # cat pre_abl_time
>> 2879 ms
>>
>> The Module Power Manager(MPM) sleep counter starts ticking at the PBL
>> stage and the timestamp generated by the sleep counter is logged by
>> the Qualcomm proprietary bootloader(ABL) at two points-> First when it
>> starts execution which is logged here as "pre_abl_time" and the second
>> when it is about to load the kernel logged as "abl_time". Documentation
>> details are also added in Documentation/ABI/testing/debugfs-driver-bootstat
>>
> 
> I would have preferred some way to implement this without spending
> countless kB of RAM to occasionally read out two u32 values...

If this is just for the debug build, why we are caring of it. There are 
various others kernel features we enable to debug the system crashes 
which consumes lot of RAM as well. Optimizations are good, but not sure
if we need to overdo it when it is just for debugging.

---Trilok Soni