linux-kernel - Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need

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Message-ID: <20231202184507.26178c17@rorschach.local.home>
Date:   Sat, 2 Dec 2023 18:45:07 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, rcu@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need_qs value
 incorrect likely()?

On Sat, 2 Dec 2023 14:24:26 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > Note, the unlikely tracing is running on my production server v6.6.3.
> > 
> > The above trace is from my test box with latest Linus's tree.  
> 
> Nice tool!!!

Thanks! It's only been in the kernel since 2008 ;-)

  1f0d69a9fc815 ("tracing: profile likely and unlikely annotations")

> 
> My kneejerk reaction is that that condition is suboptimal.  Does the 
> (untested) patch below help things?

I'll give it a try on Monday.

Thanks,

-- Steve