* [PATCH for-v7.5 4/5] rcu-tasks: Use pr_debug() for callback contend/collapse messages
[not found] <20261113004946.2758197-1-jfern@kernel.org>
@ 2026-11-13 0:49 ` Joel Fernandes
2026-11-13 1:01 ` Joel Fernandes
0 siblings, 1 reply; 2+ messages in thread
From: Joel Fernandes @ 2026-11-13 0:49 UTC (permalink / raw)
To: linux-kernel, Paul E . McKenney, Frederic Weisbecker,
Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng,
Uladzislau Rezki, Steven Rostedt, Mathieu Desnoyers,
Lai Jiangshan, Zqiang, Jonathan Corbet, Shuah Khan, Randy Dunlap
Cc: rcu, Song Liu, linux-doc
From: Song Liu <song@kernel.org>
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@kernel.org>
Signed-off-by: Joel Fernandes <jfern@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 7 -------
kernel/rcu/tasks.h | 15 +++------------
2 files changed, 3 insertions(+), 19 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0b3c140babd9..176648941aec 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6369,13 +6369,6 @@ Kernel parameters
period to instead use normal non-expedited
grace-period processing.
- rcupdate.rcu_task_collapse_debug= [KNL]
- Enable debugging prints that record when RCU Tasks
- and RCU Tasks Trace expand to per-CPU callback
- queuing and collapse back to CPU-0 queuing.
- This is default-disabled due to the fact that
- some workloads can make it quite noisy.
-
rcupdate.rcu_task_collapse_lim= [KNL]
Set the maximum number of callbacks present
at the beginning of a grace period that allows
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index a59aa8b6ab05..0eec90464d64 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -178,8 +178,6 @@ static int rcu_task_contend_lim __read_mostly = 100;
module_param(rcu_task_contend_lim, int, 0444);
static int rcu_task_collapse_lim __read_mostly = 10;
module_param(rcu_task_collapse_lim, int, 0444);
-static bool rcu_task_collapse_debug __read_mostly;
-module_param(rcu_task_collapse_debug, bool, 0644);
static int rcu_task_lazy_lim __read_mostly = 32;
module_param(rcu_task_lazy_lim, int, 0444);
@@ -392,8 +390,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
WRITE_ONCE(rtp->percpu_enqueue_shift, 0);
WRITE_ONCE(rtp->percpu_dequeue_lim, rcu_task_cpu_ids);
smp_store_release(&rtp->percpu_enqueue_lim, rcu_task_cpu_ids);
- if (data_race(rcu_task_collapse_debug))
- pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name);
+ pr_debug("Switching %s to per-CPU callback queuing.\n", rtp->name);
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
}
@@ -514,9 +511,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
smp_store_release(&rtp->percpu_enqueue_lim, 1);
rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu();
gpdone = false;
- if (data_race(rcu_task_collapse_debug))
- pr_info("Starting switch %s to CPU-0 callback queuing.\n",
- rtp->name);
+ pr_debug("Starting switch %s to CPU-0 callback queuing.\n", rtp->name);
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
}
@@ -524,9 +519,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) {
WRITE_ONCE(rtp->percpu_dequeue_lim, 1);
- if (data_race(rcu_task_collapse_debug))
- pr_info("Completing switch %s to CPU-0 callback queuing.\n",
- rtp->name);
+ pr_debug("Completing switch %s to CPU-0 callback queuing.\n", rtp->name);
}
if (rtp->percpu_dequeue_lim == 1) {
for (cpu = rtp->percpu_dequeue_lim; cpu < rcu_task_cpu_ids; cpu++) {
@@ -711,8 +704,6 @@ static void __init rcu_tasks_bootup_oddness(void)
pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc);
rcu_task_stall_info_mult = rtsimc;
}
- if (rcu_task_collapse_debug)
- pr_info("\tTasks-RCU callback contend/collapse debug enabled.\n");
#endif /* #ifdef CONFIG_TASKS_RCU */
#ifdef CONFIG_TASKS_RCU
pr_info("\tTrampoline variant of Tasks RCU enabled.\n");
--
2.54.0
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