linux-kernel - Re: [RFC PATCH 03/11] sched: Add sched tracepoints for RV task model

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Message-ID: <20250206085738.GL7145@noisy.programming.kicks-ass.net>
Date: Thu, 6 Feb 2025 09:57:38 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 03/11] sched: Add sched tracepoints for RV task model

On Thu, Feb 06, 2025 at 09:36:41AM +0100, Gabriele Monaco wrote:

> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index 165c90ba64ea9..fb5f8aa61ef5d 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -491,6 +491,12 @@ sched_core_dequeue(struct rq *rq, struct
> > > task_struct *p, int flags) { }
> > >  
> > >  #endif /* CONFIG_SCHED_CORE */
> > >  
> > > +void trace_set_current_state(int state_value)
> > > +{
> > > +	trace_sched_set_state_tp(current, current->__state,
> > > state_value);
> > > +}
> > > +EXPORT_SYMBOL(trace_set_current_state);
> > 
> > Urgh, why !?!
> > 
> 
> Do you mean why exporting it?
> At first I was puzzled too (this line is borrowed from Daniel), but the
> thing is: set_current_state and friends are macros called by any sort
> of code (e.g. modules), this seems the easiest way without messing up
> with the current code.
> 
> I'm not sure if it would be cleaner to just drop this function and
> define it directly in the header (including also trace/events/sched.h
> there). It felt like files including sched shouldn't know about
> tracepoints.
> 
> What do you think would be better?

So I would think having the tracepoint in-line would be better. Because
as is, everything gets to have this pointless CALL to an empty function.

If this were x86_64 only, I would suggest using static_call(), but
barring that, the static_branch() already in the tracepoint is the best
we can do.