linux-kernel - Re: [PATCH v3] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE

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Message-ID: <09c76498-6a0b-4880-8a86-2a295c47c703@efficios.com>
Date: Fri, 12 Dec 2025 23:19:41 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>,
 "Paul E. McKenney" <paulmck@...nel.org>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
 Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3] tracing: Guard __DECLARE_TRACE() use of
 __DO_TRACE_CALL() with SRCU-fast

On 2025-12-12 21:18, Steven Rostedt wrote:
[...]
> 
> Thus, I'm going to keep this a PREEMPT_RT only change. If someone can
> come in and convince us that the PREEMPT_RT way is also beneficial for
> the non-RT case then we can make it consistent again. Until then, this
> change is focusing on fixing PREEMPT_RT, and that's what the patch is
> going to be limited to.

Here is one additional thing to keep in mind: although
SRCU-fast is probably quite fast (as the name implies),
last time I tried using migrate disable in a fast path
I was surprised to see verbosity of the generated assembly,
and how slow it was compared to preempt disable.

So before using migrate disable on a fast path, at least on
non-preempt-RT configs, we should carefully consider the
performance impact of migrate disable.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com