Re: [RCU] rcu_tasks_trace_qs(): trc_reader_special.b.need_qs value incorrect likely()?

[Steven Rostedt]

On Sat, 2 Dec 2023 18:45:07 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

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

-- Steve