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

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Message-ID: <20260109170028.0068a14d@fedora>
Date: Fri, 9 Jan 2026 17:00:28 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.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>
Subject: Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of
 __DO_TRACE_CALL() with SRCU-fast

On Fri, 9 Jan 2026 13:54:34 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Fri, Jan 9, 2026 at 12:21 PM Mathieu Desnoyers
> <mathieu.desnoyers@...icios.com> wrote:
> >
> >
> > * preempt disable/enable pair:                                     1.1 ns
> > * srcu-fast lock/unlock:                                           1.5 ns
> >
> > CONFIG_RCU_REF_SCALE_TEST=y
> > * migrate disable/enable pair:                                     3.0 ns  
> 
> .. and you're arguing that 3ns vs 1ns difference is so important
> for your out-of-tree tracer that in-tree tracers need to do
> some workarounds?! wtf

This has nothing to do with out of tree tracers. The overhead of the
22ns is for any tracepoint in an in-tree module. That's because the
rq->nr_pinned isn't exported for modules to use.

-- Steve