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

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Message-ID: <20260109141930.6deb2a0a@gandalf.local.home>
Date: Fri, 9 Jan 2026 14:19:30 -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 11:10:16 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

\> >
> > We also have to consider that migrate disable is *not* cheap at all
> > compared to preempt disable.  
> 
> Looks like your complaint comes from lack of engagement in kernel
> development.

No need to make comments like that. The Linux kernel is an ocean of code.
It's very hard to keep up on everything that is happening. I knew of work
being done on migrate_disable but I didn't know what the impacts of that
work was. Mathieu is still very much involved and engaged in kernel
development.

> migrate_disable _was_ not cheap.
> Try to benchmark it now.
> It's inlined. It's a fraction of extra overhead on top of preempt_disable.

It would be good to have a benchmark of the two. What about fast_srcu? Is
that fast enough to replace the preempt_disable()? If so, then could we
just make this the same for both RT and !RT?

-- Steve