linux-kernel - Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE

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Message-ID: <20260112154410.GA830229@noisy.programming.kicks-ass.net>
Date: Mon, 12 Jan 2026 16:44:10 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>,
	bpf <bpf@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of
 __DO_TRACE_CALL() with SRCU-fast

On Mon, Jan 12, 2026 at 10:36:12AM -0500, Steven Rostedt wrote:
> On Mon, 12 Jan 2026 16:31:28 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > OUCH! So migrate disable/enable has a much larger overhead when executed in
> > > a module than in the kernel? This means all spin_locks() in modules
> > > converted to mutexes in PREEMPT_RT are taking this hit!  
> > 
> > Not so, the migrate_disable() for PREEMPT_RT is still in core code --
> > kernel/locking/spinlock_rt.c is very much not build as a module.
> 
> True. But still, wouldn't it be cleaner to have that variable separate from
> the run queue and make the code a bit simpler?

I still don't like exporting variables either way around. Exporting
functions is much saner.