linux-kernel - Re: [PATCH V2 2/3] soc: qcom: boot_stat: Add Driver Support for Boot Stats

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Message-ID: <d260f351-1cf1-aecc-e8f5-d0877ed04ab6@quicinc.com>
Date:   Wed, 12 Apr 2023 19:52:01 +0530
From:   Souradeep Chowdhury <quic_schowdhu@...cinc.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>
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 V2 2/3] soc: qcom: boot_stat: Add Driver Support for Boot
 Stats



On 4/12/2023 1:47 PM, Krzysztof Kozlowski wrote:
> On 10/04/2023 08:48, Souradeep Chowdhury wrote:
>>
>>
>> On 4/7/2023 9:11 PM, Bjorn Andersson wrote:
>>> On Fri, Apr 07, 2023 at 07:34:36PM +0530, 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 print the information. This information is
>>>> useful in verifying if the existing boot KPIs have regressed or not.
>>>> A sample log in SM8450(waipio) device is as follows:-
>>>>
>>>> KPI: Pre ABL Time = 3s
>>>> KPI: ABL Time = 14s
>>>
>>> Why are these in whole seconds?
>>
>> This is to give a granular view of time.
>>
>>>
>>>> KPI: Kernel MPM timestamp = 890206
>>>
>>> And why is this presented in cycles?
>>
>> This timestamp is used as an intermediate value for calculating one of
>> the KPIs. Can be changed to seconds as well for consistency.
>>
>>>
>>>>
>>>> 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". Both are
>>>> logged in the unit of seconds.
>>>
>>> We have a policy to not taint the kernel log with "useless" information,
>>> for kernel developers this seems to add no value and for end users
>>> there's no benefit to this.
>>>
>>>> The current kernel timestamp is
>>>> printed by the boot_stats driver as well.
>>>>
>>>
>>> Why?
>>
>> Same as stated above.
> 
> You did not answer. The question is "why do you think printing this
> during boot is suitable for wide usage?". I don't find answer "give a
> granular view of time" anyway related.
> 
> Please come with rationale why such printing should be used in Linux
> kernel at all, given that as Bjorn said - we do not print
> debugging/profiling information.
> 
> You should probably come with a debugfs interface for this.

Ack. The debugfs interface for this will be present in the next version.

> 
> Best regards,
> Krzysztof
>