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Message-Id: <20211202003858.3129628-3-paulmck@kernel.org>
Date: Wed, 1 Dec 2021 16:38:43 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
jiangshanlai@...il.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...icios.com, josh@...htriplett.org,
tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...nel.org>, Martin Lau <kafai@...com>,
Neeraj Upadhyay <neeraj.iitr10@...il.com>
Subject: [PATCH rcu 03/18] rcu-tasks: Introduce ->percpu_enqueue_shift for dynamic queue selection
This commit introduces a ->percpu_enqueue_shift field to the rcu_tasks
structure, and uses it to shift down the CPU number in order to
select a rcu_tasks_percpu structure. This field is currently set to a
sufficiently large shift count to always select the CPU-0 instance of
the rcu_tasks_percpu structure, and later commits will adjust this.
Reported-by: Martin Lau <kafai@...com>
Cc: Neeraj Upadhyay <neeraj.iitr10@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
kernel/rcu/tasks.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 30048db7aa49d..2a5fe3e04b363 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -52,6 +52,7 @@ struct rcu_tasks_percpu {
* @postgp_func: This flavor's post-grace-period function (optional).
* @call_func: This flavor's call_rcu()-equivalent function.
* @rtpcpu: This flavor's rcu_tasks_percpu structure.
+ * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
* @name: This flavor's textual name.
* @kname: This flavor's kthread name.
*/
@@ -75,6 +76,7 @@ struct rcu_tasks {
postgp_func_t postgp_func;
call_rcu_func_t call_func;
struct rcu_tasks_percpu __percpu *rtpcpu;
+ int percpu_enqueue_shift;
char *name;
char *kname;
};
@@ -91,6 +93,7 @@ static struct rcu_tasks rt_name = \
.call_func = call, \
.rtpcpu = &rt_name ## __percpu, \
.name = n, \
+ .percpu_enqueue_shift = ilog2(CONFIG_NR_CPUS), \
.kname = #rt_name, \
}
@@ -169,6 +172,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
unsigned long flags;
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
+ rtp->percpu_enqueue_shift = ilog2(nr_cpu_ids);
for_each_possible_cpu(cpu) {
struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
@@ -195,7 +199,8 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
rhp->next = NULL;
rhp->func = func;
local_irq_save(flags);
- rtpcp = per_cpu_ptr(rtp->rtpcpu, 0 /* smp_processor_id() */);
+ rtpcp = per_cpu_ptr(rtp->rtpcpu,
+ smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift));
raw_spin_lock(&rtpcp->cbs_pcpu_lock);
if (!rtpcp->cbs_tail) {
raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.
--
2.31.1.189.g2e36527f23
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