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rcu-tasks: Add rcupdate.rcu_task_enqueue_lim to set initial queueing

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This commit adds a rcupdate.rcu_task_enqueue_lim module parameter that
sets the initial number of callback queues to use for the RCU Tasks
family of RCU implementations.  This parameter allows testing of various
fanout values.

Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-11-12 07:33:40 -08:00
parent ce9b1c667f
commit 8610b65680
2 changed files with 25 additions and 6 deletions
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7
Documentation/admin-guide/kernel-parameters.txt
View File

@ -4805,6 +4805,13 @@
period to instead use normal non-expedited
grace-period processing.
rcupdate.rcu_task_enqueue_lim= [KNL]
Set the number of callback queues to use for the
RCU Tasks family of RCU flavors. The default
of -1 allows this to be automatically (and
dynamically) adjusted. This parameter is intended
for use in testing.
rcupdate.rcu_task_ipi_delay= [KNL]
Set time in jiffies during which RCU tasks will
avoid sending IPIs, starting with the beginning

24
kernel/rcu/tasks.h
View File

@ -130,6 +130,9 @@ module_param(rcu_task_ipi_delay, int, 0644);
static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
module_param(rcu_task_stall_timeout, int, 0644);
static int rcu_task_enqueue_lim __read_mostly = -1;
module_param(rcu_task_enqueue_lim, int, 0444);
/* RCU tasks grace-period state for debugging. */
#define RTGS_INIT 0
#define RTGS_WAIT_WAIT_CBS 1
@ -192,10 +195,19 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
{
int cpu;
unsigned long flags;
int lim;
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
rtp->percpu_enqueue_shift = ilog2(nr_cpu_ids);
rtp->percpu_enqueue_lim = 1;
if (rcu_task_enqueue_lim < 0)
rcu_task_enqueue_lim = nr_cpu_ids;
else if (rcu_task_enqueue_lim == 0)
rcu_task_enqueue_lim = 1;
lim = rcu_task_enqueue_lim;
if (lim > nr_cpu_ids)
lim = nr_cpu_ids;
WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids / lim));
smp_store_release(&rtp->percpu_enqueue_lim, lim);
for_each_possible_cpu(cpu) {
struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
@ -211,7 +223,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
}
raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
}
// Enqueue a callback for the specified flavor of Tasks RCU.
@ -307,7 +319,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
unsigned long flags;
int needgpcb = 0;
for (cpu = 0; cpu < rtp->percpu_enqueue_lim; cpu++) {
for (cpu = 0; cpu < smp_load_acquire(&rtp->percpu_enqueue_lim); cpu++) {
struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
/* Advance and accelerate any new callbacks. */
@ -338,11 +350,11 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
cpu = rtpcp->cpu;
cpunext = cpu * 2 + 1;
if (cpunext < rtp->percpu_enqueue_lim) {
if (cpunext < smp_load_acquire(&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) {
if (cpunext < smp_load_acquire(&rtp->percpu_enqueue_lim)) {
rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work);
}