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Message-Id: <20211202003858.3129628-4-paulmck@kernel.org>
Date: Wed, 1 Dec 2021 16:38:44 -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 04/18] rcu-tasks: Convert grace-period counter to grace-period sequence number
This commit moves the rcu_tasks structure's ->n_gps grace-period-counter
field to a ->task_gp_seq grce-period sequence number in order to enable
use of the rcu_segcblist structure for the callback lists. This in turn
permits CPUs to lag behind the RCU Tasks grace-period sequence number
without suffering long-term slowdowns in callback invocation.
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 | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 2a5fe3e04b363..ed84d59b6dbfa 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -42,7 +42,7 @@ struct rcu_tasks_percpu {
* @init_fract: Initial backoff sleep interval.
* @gp_jiffies: Time of last @gp_state transition.
* @gp_start: Most recent grace-period start in jiffies.
- * @n_gps: Number of grace periods completed since boot.
+ * @tasks_gp_seq: Number of grace periods completed since boot.
* @n_ipis: Number of IPIs sent to encourage grace periods to end.
* @n_ipis_fails: Number of IPI-send failures.
* @pregp_func: This flavor's pre-grace-period function (optional).
@@ -64,7 +64,7 @@ struct rcu_tasks {
int init_fract;
unsigned long gp_jiffies;
unsigned long gp_start;
- unsigned long n_gps;
+ unsigned long tasks_gp_seq;
unsigned long n_ipis;
unsigned long n_ipis_fails;
struct task_struct *kthread_ptr;
@@ -273,8 +273,9 @@ static int __noreturn rcu_tasks_kthread(void *arg)
// Wait for one grace period.
set_tasks_gp_state(rtp, RTGS_WAIT_GP);
rtp->gp_start = jiffies;
+ rcu_seq_start(&rtp->tasks_gp_seq);
rtp->gp_func(rtp);
- rtp->n_gps++;
+ rcu_seq_end(&rtp->tasks_gp_seq);
/* Invoke the callbacks. */
set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
@@ -335,7 +336,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
rtp->kname,
tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
jiffies - data_race(rtp->gp_jiffies),
- data_race(rtp->n_gps),
+ data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
".k"[!!data_race(rtp->kthread_ptr)],
".C"[!!data_race(rtpcp->cbs_head)],
--
2.31.1.189.g2e36527f23
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