linux-kernel - Re: [PATCH 2/3] tracing: Use in_serving

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Date:   Fri, 22 Jan 2021 17:11:25 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/3] tracing: Use in_serving_softirq() to deduct softirq
 status.

On Wed, 13 Jan 2021 00:00:56 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> Use in_serving_softirq() macro which works on PREEMPT_RT. On !PREEMPT_RT
> the compiler (gcc-10 / clang-11) is smart enough to optimize the
> in_serving_softirq() related read of the preemption counter away.
> The only difference I noticed by using in_serving_softirq() on
> !PREEMPT_RT is that gcc-10 implemented tracing_gen_ctx_flags() as
> reading FLAG, jmp _tracing_gen_ctx_flags(). Without in_serving_softirq()
> it inlined _tracing_gen_ctx_flags() into tracing_gen_ctx_flags().

If we inline it normally (as described in my first patch reply), there may
be no difference.

-- Steve