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Date: Wed, 1 Dec 2021 16:38:51 -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 11/18] rcu-tasks: Use workqueues for multiple rcu_tasks_invoke_cbs() invocations
If there is a flood of callbacks, it is necessary to put multiple
CPUs to work invoking those callbacks. This commit therefore uses a
workqueue-flooding approach to parallelize RCU Tasks callback execution.
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 | 77 +++++++++++++++++++++++++++++++---------------
1 file changed, 53 insertions(+), 24 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 3bc0edb6a7bb6..a75a4ca78a621 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -24,10 +24,14 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
* struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.
* @cblist: Callback list.
* @lock: Lock protecting per-CPU callback list.
+ * @rtp_work: Work queue for invoking callbacks.
*/
struct rcu_tasks_percpu {
struct rcu_segcblist cblist;
raw_spinlock_t __private lock;
+ struct work_struct rtp_work;
+ int cpu;
+ struct rcu_tasks *rtpp;
};
/**
@@ -146,6 +150,8 @@ static const char * const rcu_tasks_gp_state_names[] = {
//
// Generic code.
+static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp);
+
/* Record grace-period phase and time. */
static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
{
@@ -185,6 +191,9 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
if (rcu_segcblist_empty(&rtpcp->cblist))
rcu_segcblist_init(&rtpcp->cblist);
+ INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq);
+ rtpcp->cpu = cpu;
+ rtpcp->rtpp = rtp;
raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
@@ -257,36 +266,56 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
}
// Advance callbacks and invoke any that are ready.
-static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp)
+static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp)
{
int cpu;
+ int cpunext;
unsigned long flags;
int len;
- struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
struct rcu_head *rhp;
-
- for (cpu = 0; cpu < rtp->percpu_enqueue_lim; cpu++) {
- struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
-
- if (rcu_segcblist_empty(&rtpcp->cblist))
- continue;
- raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
- smp_mb__after_spinlock(); // Order updates vs. GP.
- rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
- rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl);
- raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
- len = rcl.len;
- for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
- local_bh_disable();
- rhp->func(rhp);
- local_bh_enable();
- cond_resched();
+ struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
+ struct rcu_tasks_percpu *rtpcp_next;
+
+ cpu = rtpcp->cpu;
+ cpunext = cpu * 2 + 1;
+ if (cpunext < rtp->percpu_enqueue_lim) {
+ rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
+ queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work);
+ cpunext++;
+ if (cpunext < rtp->percpu_enqueue_lim) {
+ rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
+ queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work);
}
- raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
- rcu_segcblist_add_len(&rtpcp->cblist, -len);
- (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
- raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
}
+
+ if (rcu_segcblist_empty(&rtpcp->cblist))
+ return;
+ raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
+ smp_mb__after_spinlock(); // Order updates vs. GP.
+ rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
+ rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl);
+ raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
+ len = rcl.len;
+ for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+ local_bh_disable();
+ rhp->func(rhp);
+ local_bh_enable();
+ cond_resched();
+ }
+ raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
+ rcu_segcblist_add_len(&rtpcp->cblist, -len);
+ (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
+ raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
+}
+
+// Workqueue flood to advance callbacks and invoke any that are ready.
+static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp)
+{
+ struct rcu_tasks *rtp;
+ struct rcu_tasks_percpu *rtpcp = container_of(wp, struct rcu_tasks_percpu, rtp_work);
+
+ rtp = rtpcp->rtpp;
+ rcu_tasks_invoke_cbs(rtp, rtpcp);
}
/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
@@ -322,7 +351,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
/* Invoke callbacks. */
set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
- rcu_tasks_invoke_cbs(rtp);
+ rcu_tasks_invoke_cbs(rtp, per_cpu_ptr(rtp->rtpcpu, 0));
/* Paranoid sleep to keep this from entering a tight loop */
schedule_timeout_idle(rtp->gp_sleep);
--
2.31.1.189.g2e36527f23
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