linux-kernel - Re: [PATCH] rcu: ftrace: avoid tracing a few functions executed in multi_cpu

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Date:   Fri, 22 Apr 2022 11:52:34 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     patrick wang <patrick.wang.shcn@...il.com>
Cc:     paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: ftrace: avoid tracing a few functions executed in
 multi_cpu_stop()

On Fri, 22 Apr 2022 18:45:46 +0800
patrick wang <patrick.wang.shcn@...il.com> wrote:

> Yes, and not just RISC-V. It's arch-independent. It's the internal change of
> stop machine implementation.
> 
> ----------------------------------------------------------------
> Former stop machine wait loop:
> do {
>     cpu_relax(); => macro
>     ...
> } while (curstate != STOPMACHINE_EXIT);
> -----------------------------------------------------------------
> Current stop machine wait loop:
> do {
>     stop_machine_yield(cpumask); => function (notraced)
>     ...
>     touch_nmi_watchdog(); => function (notraced, inside calls also notraced)
>     ...
>     rcu_momentary_dyntick_idle(); => function (notraced, inside calls traced)
> } while (curstate != MULTI_STOP_EXIT);
> ------------------------------------------------------------------

That makes much more sense. Can you add that to the change log.

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve