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Date: Thu, 5 Mar 2026 18:42:23 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Dmitry Ilvokhin <d@ilvokhin.com>, Dennis Zhou <dennis@kernel.org>,
	Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@gentwo.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
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	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org, kernel-team@meta.com
Subject: Re: [PATCH RFC 3/3] locking: Wire up contended_release tracepoint
Message-ID: <20260305174223.GA1442992@noisy.programming.kicks-ass.net>
References: <cover.1772642407.git.d@ilvokhin.com>
 <8298e098d3418cb446ef396f119edac58a3414e9.1772642407.git.d@ilvokhin.com>
 <20260305105924.7069eb23@gandalf.local.home>
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In-Reply-To: <20260305105924.7069eb23@gandalf.local.home>

On Thu, Mar 05, 2026 at 10:59:24AM -0500, Steven Rostedt wrote:
> On Wed,  4 Mar 2026 16:56:17 +0000
> Dmitry Ilvokhin <d@ilvokhin.com> wrote:
> 
> > @@ -204,6 +206,8 @@ static inline void rwbase_write_unlock(struct rwbase_rt *rwb)
> >  	unsigned long flags;
> >  
> >  	raw_spin_lock_irqsave(&rtm->wait_lock, flags);
> > +	if (rt_mutex_has_waiters(rtm))
> > +		trace_contended_release(rwb);
> 
> Hmm, if statements should never be used just for tracepoints without a
> static branch. The above should be:
> 
> 	if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm))
> 		trace_contended_release(rwb);
> 

I still wish you would accept:

	if (trace_foo_enabled() && foo)
		__do_trace_foo();

The compilers can't optimize the static branches and thus you'll get it
twice for no reason.

I really wish they would just accept __pure, but alas.