linux-kernel - Re: [PATCH V3 1/2] tick: Rename tick_do_update

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Message-ID: <873509e98n.ffs@tglx>
Date:   Wed, 23 Aug 2023 23:31:36 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Huacai Chen <chenhuacai@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Cc:     Alan Huang <mmpgouride@...il.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/2] tick: Rename tick_do_update_jiffies64() and
 allow external usage

On Sun, Aug 13 2023 at 21:22, Huacai Chen wrote:
> On Sun, Aug 13, 2023 at 10:07 AM Joel Fernandes <joel@...lfernandes.org> wrote:
>> For the RCU part, looks fine to me.
>>
>> Another option for the jiffies update part is to just expose a wrapper
>> around the main update function and use that wrapper.
>> That way you do not need to move a lot of code and that keeps git
>> blame intact.
>
> Thank you for your review. But since tick_do_update_jiffies64() is
> static and tick-sched.c itself is conditionally compiled. It seems
> impossible to make a wrapper without touching the original function.

That's just wrong.

tick-sched.o depends on CONFIG_TICK_ONESHOT

do_update_jiffies_64() is only doing anything when

  CONFIG_NO_HZ_COMMON=y or CONFIG_HIGH_RES_TIMERS=y

CONFIG_NO_HZ_COMMON selects CONFIG_TICK_ONESHOT
CONFIG_HIGH_RES_TIMERS selects CONFIG_TICK_ONESHOT

So what is that code move solving?

Absolutely nothing, because when CONFIG_TICK_ONESHOT is not set, then
neither CONFIG_NO_HZ_COMMON nor CONFIG_HIGH_RES_TIMERS is set and the
invocation of tick_do_update_jiffies64() is just a NOOP.

So the code stays where it is and all it takes is to remove the static
and to provide a stub inline function for the CONFIG_TICK_ONESHOT=n
case, no?

Thanks,

        tglx