linux-kernel - Re: [PATCH v3 08/22] rcu,tracing: Create trace_rcu

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Message-ID: <20200219163535.GJ18400@hirez.programming.kicks-ass.net>
Date:   Wed, 19 Feb 2020 17:35:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v3 08/22] rcu,tracing: Create trace_rcu_{enter,exit}()

On Wed, Feb 19, 2020 at 11:15:32AM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2020 16:58:28 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, Feb 19, 2020 at 10:49:03AM -0500, Steven Rostedt wrote:
> > > On Wed, 19 Feb 2020 15:47:32 +0100
> > > Peter Zijlstra <peterz@...radead.org> wrote:  
> > 
> > > > These helpers are macros because of header-hell; they're placed here
> > > > because of the proximity to nmi_{enter,exit{().  
> > 
> > ^^^^
> 
> Bah I can't read, because I even went looking for this!
> 
> > 
> > > > +#define trace_rcu_enter()					\
> > > > +({								\
> > > > +	unsigned long state = 0;				\
> > > > +	if (!rcu_is_watching())	{				\
> > > > +		rcu_irq_enter_irqsave();			\
> > > > +		state = 1;					\
> > > > +	}							\
> > > > +	state;							\
> > > > +})
> > > > +
> > > > +#define trace_rcu_exit(state)					\
> > > > +do {								\
> > > > +	if (state)						\
> > > > +		rcu_irq_exit_irqsave();				\
> > > > +} while (0)
> > > > +  
> > > 
> > > Is there a reason that these can't be static __always_inline functions?  
> > 
> > It can be done, but then we need fwd declarations of those RCU functions
> > somewhere outside of rcupdate.h. It's all a bit of a mess.
> 
> Maybe this belongs in the rcupdate.h file then?

Possibly, and I suppose the current version is less obviously dependent
on the in_nmi() functionality as was the previous, seeing how Paul
frobbed that all the way into the rcu_irq_enter*() implementation.

So sure, I can go move it I suppose.