Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast

[Steven Rostedt]

On Fri, 9 Jan 2026 17:33:26 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> How is this about lttng? Sure he cares about that, but even tracepoints
> that lttng uses doesn't get affected any more than ftrace or bpf.
> Because lttng is one of the callbacks. The migrate disable happens in
> the in-tree portion of the code.
> 
> So you are saying that all the tracepoints for xfs are not in a fastpath?

Regardless of tracing. I now have my RT hat on. The spin_locks that are
converted to mutex use migrate disable. The fact that migrate_disable
in modules are close to 10x slower than the same code in-kernel is
troubling to say the least. It means that modules in RT take a hit
every time they take a spin_lock().

The migrate disable being slow for modules is no longer just a tracing
issue. It's a PREEMPT_RT issue.

-- Steve