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Date:   Tue, 5 Dec 2023 15:59:27 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, rcu@vger.kernel.org,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need_qs value
 incorrect likely()?
Message-ID: <20231205155927.4b3b9151@gandalf.local.home>
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        <b0772bf3-5b47-4aea-b964-17a2bebc6313@paulmck-laptop>
        <20231202184507.26178c17@rorschach.local.home>
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On Sat, 2 Dec 2023 18:45:07 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

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

This looks to have caused a difference. Although there's other RCU
functions that need dealing with, but that's for when I have time to
analyze all the places that have bad annotations.


Anyway:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
 [..]
   17924        0   0 rcu_softirq_qs                 tree.c               247

Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve