Re: [PATCH] rcu-tasks: Use pr_debug() for callback contend/collapse messages

[Paul E. McKenney]

On Wed, Nov 11, 2026 at 06:22:21PM +0000, Joel Fernandes wrote:
> 
> 
> > On Nov 11, 2026, at 12:32 PM, Song Liu <song@xxxxxxxxxx> wrote:
> > 
> > On Wed, Nov 11, 2026 at 7:54 AM Joel Fernandes <joelagnelf@xxxxxxxxxx> 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 <song@xxxxxxxxxx>
> >> 
> >> Makes sense to me,
> >> 
> >> Reviewed-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
> >> 
> >> 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