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

[Souradeep Chowdhury]

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