Re: [PATCH RFC ftrace] Chose RCU Tasks based on TASKS_RCU rather than PREEMPTION

[Paul E. McKenney]

On Fri, Mar 01, 2024 at 03:30:01PM -0500, Steven Rostedt wrote:
> On Fri, 1 Mar 2024 12:25:10 -0800
> "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
> 
> > > That would work for me.  If there are no objections, I will make this
> > > change.  
> > 
> > But I did check the latency of synchronize_rcu_tasks_rude() (about 100ms)
> > and synchronize_rcu() (about 20ms).  This is on a 80-hardware-thread
> > x86 system that is being flooded with calls to one or the other of
> > these two functions, but is otherwise idle.  So adding that unnecessary
> > synchronize_rcu() adds about 20% to that synchronization delay.
> > 
> > Which might still be OK, but...  In the immortal words of MS-DOS,
> > "Are you sure?".  ;-)
> 
> It's just safe to keep it. It's definitely not a fast path.

OK, you got it!  ;-)

							Thanx, Paul