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McKenney" To: Joel Fernandes Cc: Song Liu , "rcu@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kernel-team@meta.com" , "rostedt@goodmis.org" , "leitao@debian.org" , "david.dai@linux.dev" Subject: Re: [PATCH] rcu-tasks: Use pr_debug() for callback contend/collapse messages Message-ID: <94f4f310-63f2-4964-bca3-e1756901d33a@paulmck-laptop> Reply-To: paulmck@kernel.org References: <20261111053551.3367903-1-song@kernel.org> <20261111155441.GA1829883@joelbox> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Nov 11, 2026 at 06:22:21PM +0000, Joel Fernandes wrote: > > > > On Nov 11, 2026, at 12:32 PM, Song Liu wrote: > > > > On Wed, Nov 11, 2026 at 7:54 AM Joel Fernandes wrote: > >> > >>> On Tue, Nov 10, 2026 at 09:35:51PM -0800, Song Liu wrote: > >>> Commit 5de907d24919 ("rcu-tasks: Disable callback contend/collapse > >>> messages by default") added the rcupdate.rcu_task_collapse_debug module > >>> parameter to gate the three pr_info() messages that report RCU Tasks > >>> switching between CPU-0 and per-CPU callback queuing. > >>> > >>> The kernel already has a mechanism for debug-only messages that are off > >>> by default: pr_debug(). Use pr_debug() for these messages, and remove > >>> the rcu_task_collapse_debug module parameter, its documentation, and > >>> its boot-time announcement. > >>> > >>> The messages stay off by default. On CONFIG_DYNAMIC_DEBUG=y kernels, > >>> they can be enabled at boot with: > >>> > >>> dyndbg="file kernel/rcu/tasks.h +p" > >>> > >>> or at runtime with: > >>> > >>> echo 'file kernel/rcu/tasks.h +p' > /proc/dynamic_debug/control > >>> > >>> Assisted-by: Claude:claude-opus-5 > >>> Signed-off-by: Song Liu > >> > >> Makes sense to me, > >> > >> Reviewed-by: Joel Fernandes > >> > >> Will apply for 7.5. > > > > How about we queue this for 7.4, say rc3 or rc4. > > > > If we delay until 7.5, 7.4 kernel will be the only one that has > > rcupdate.rcu_task_collapse_debug. IOW, if we merge it to 7.4, > > no official kernel will have rcupdate.rcu_task_collapse_debug > > at all. > > > > WDYT? > > That works for me, Paul shall I send this one separately for the -rc? Also appreciate an Reviewed by tag from your side. I sent the Reviewed-by directly in response to Song's patch, and I would be happy for you to send the pull request. ;-) Thanx, Paul