Re: [PATCH v3 2/2] tracing: Remove trace_printk.h from kernel.h

[David Laight]

On Wed, 24 Jun 2026 10:32:25 -0400
Steven Rostedt <rostedt@xxxxxxxxxx> wrote:

> On Wed, 24 Jun 2026 11:11:52 +0100
> David Laight <david.laight.linux@xxxxxxxxx> wrote:
> 
> > That is all about changes to the file causing everything to be rebuilt,
> > not the contents of the file slowing down builds.  
> 
> I guess I should say it better. It causes more build time if that file
> changes. That's what I meant. I update the wording to say:
> 
>    There have been complaints about trace_printk.h causing more build time
>    for being in kernel.h it if changes. There is also an effort to clean up
>    kernel.h to have it not include unneeded header files. Move trace_printk.h
>    out of kernel.h and place it in the headers and C files that use it.
> > 
> > The part you are moving out of normal builds is just a few #defines.
> > They won't have a significant effect on build times either.
> > 
> > So there is no point splitting out trace_controls.h.  
> 
> That is a completely different reason. trace_printk.h is about
> trace_printk() usage. The stuff split out into trace_controls.h have
> nothing to do with trace_printk()s.

True, but every header file costs extra time to open.
That could easily be more that the cost of parsing it (ok hand waving!).
With a long list of -I parameters just finding a file costs because of
all the failed opens.

I've just knocked it out of kernel.h, had to fix:
	rcu.h
	linux/ftrace.h
to make my 'normal' kernel build.
Lots of stuff includes the latter.

	David

> 
> -- Steve
>