Received-SPF: pass (google.com: domain of linux-kernel+bounces-89304-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Date: Fri, 1 Mar 2024 17:54:26 -0800
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Ankur Arora <ankur.a.arora@oracle.com>,
	Thomas Gleixner <tglx@linutronix.de>, kernel-team@meta.com
Subject: Re: [PATCH RFC ftrace] Chose RCU Tasks based on TASKS_RCU rather
 than PREEMPTION
Message-ID: <fc59eb57-774a-417d-a818-afb5431b8e56@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <f6507b10-5bb5-4407-bd4d-c547193a5a28@paulmck-laptop>
 <20240228152236.7a4c9eec@gandalf.local.home>
 <b5acdc28-0441-49ca-9e8d-50d6ac40c395@paulmck-laptop>
 <2835d5ea-0396-49f6-88fb-be49cb998cc5@paulmck-laptop>
 <20240301153001.0d544f9c@gandalf.local.home>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240301153001.0d544f9c@gandalf.local.home>

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@kernel.org> 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