Re: [tip: timers/clocksource] clocksource/drivers/exynos_mct: Don't register as a sched_clock on arm64

[Daniel Lezcano]

On 24/07/2025 07:16, Ingo Molnar wrote:
> * tip-bot2 for Will McVicker <tip-bot2@xxxxxxxxxxxxx> wrote:
>
> > The following commit has been merged into the timers/clocksource branch of tip:
> >
> > Commit-ID:     394b981382e6198363cf513f6eb6be4c55b22e44
> > Gitweb:        https://git.kernel.org/tip/394b981382e6198363cf513f6eb6be4c55b22e44
> > Author:        Will McVicker <willmcvicker@xxxxxxxxxx>
> > AuthorDate:    Fri, 20 Jun 2025 11:17:05 -07:00
> > Committer:     Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > CommitterDate: Tue, 15 Jul 2025 13:00:50 +02:00
> >
> > clocksource/drivers/exynos_mct: Don't register as a sched_clock on arm64
> >
> > The MCT register is unfortunately very slow to access, but importantly
> > does not halt in the c2 idle state. So for ARM64, we can improve
> > performance by not registering the MCT for sched_clock, allowing the
> > system to use the faster ARM architected timer for sched_clock instead.
> >
> > The MCT is still registered as a clocksource, and a clockevent in order
> > to be a wakeup source for the arch_timer to exit the "c2" idle state.
> >
> > Since ARM32 SoCs don't have an architected timer, the MCT must continue
> > to be used for sched_clock. Detailed discussion on this topic can be
> > found at [1].
> >
> > [1] https://lore.kernel.org/linux-samsung-soc/1400188079-21832-1-git-send-email-chirantan@xxxxxxxxxxxx/
> >
> > [Original commit from https://android.googlesource.com/kernel/gs/+/630817f7080e92c5e0216095ff52f6eb8dd00727
> >
> > Signed-off-by: Donghoon Yu <hoony.yu@xxxxxxxxxxx>
> > Signed-off-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Reviewed-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Acked-by: John Stultz <jstultz@xxxxxxxxxx>
> > Tested-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Signed-off-by: Will McVicker <willmcvicker@xxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20250620181719.1399856-3-willmcvicker@xxxxxxxxxx
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
>
> The whole SOB chain of this commit is messy and has several serious
> problems:
>
> 1)
>
> This commit has misattributed authorship: the first SOB is:
>
>     Signed-off-by: Donghoon Yu <hoony.yu@xxxxxxxxxxx>
>
> but the Author field is not Donghoon Yu:
>
>     Author:        Will McVicker <willmcvicker@xxxxxxxxxx>

Yes, you are right. I should have pay more attention to author / sob, 
thanks for spotting it.

> 2)
>
> The Reviewed-by tag is misapplied:
>
> > Signed-off-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Reviewed-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
>
> When someone passes along a patch, it's implicit that they have
> reviewed it.

Well my understanding of the SOB chain for these is the Signed-off-by 
from Youngmin is in the delivery path because it went first to the AOSP, 
then carried on to Linux by Will. Then Reviewed-by Youngmin letting us 
know the port from AOSP to Linux is ok.

> 3)
>
> There's also a stray Tested-by tag by one of the SOB entries:
>
> > Signed-off-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Reviewed-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Tested-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
>
> When someone passes along a patch, it's implicit that they not only
> have reviewed the patch, but have also tested it to a certain extent

In this specific case where the original commit is from AOSP, this chain 
seems to make sense. Souns like:

"I was in the original commit delivery path"
"I reviewed this patch carried to Linux"
"I tested it on Linux"

> ...
>
> 4)
>
> Why is the 'Link' tag just in the middle of the SOB chain, instead at the end of it?

I don't know. Link must be at the end  It is stated somewhere in the 
documentation?

I use git b4 -s <msg-id> and the tool adds the Link then my sign off.


> Presumably this is the proper SOB chain:
>
> > Author:        Donghoon Yu <hoony.yu@xxxxxxxxxxx>
>
> > Signed-off-by: Donghoon Yu <hoony.yu@xxxxxxxxxxx>
> > Signed-off-by: Youngmin Nam <youngmin.nam@xxxxxxxxxxx>
> > Signed-off-by: Will McVicker <willmcvicker@xxxxxxxxxx>
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > Acked-by: John Stultz <jstultz@xxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20250620181719.1399856-3-willmcvicker@xxxxxxxxxx
>
> Correct?








--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog