The ilog2() function can be used to generate a shift count, but it will
generate the same count for a power of two as for one greater than a power
of two. This results in shift counts that are larger than necessary for
systems with a power-of-two number of CPUs because the CPUs are numbered
from zero, so that the maximum CPU number is one less than that power
of two.
This commit therefore substitutes order_base_2(), which appears to have
been designed for exactly this use case.
Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Martin KaFai Lau <kafai@xxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
---
kernel/rcu/tasks.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fb8c57fd70b8f..c0fc3641ef13a 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -123,7 +123,7 @@ static struct rcu_tasks rt_name = \
.call_func = call, \
.rtpcpu = &rt_name ## __percpu, \
.name = n, \
- .percpu_enqueue_shift = ilog2(CONFIG_NR_CPUS) + 1, \
+ .percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \
.percpu_enqueue_lim = 1, \
.percpu_dequeue_lim = 1, \
.barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \
@@ -302,7 +302,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
if (unlikely(needadjust)) {
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
if (rtp->percpu_enqueue_lim != nr_cpu_ids) {
- WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids) + 1);
+ WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids));
WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids);
smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids);
pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name);
@@ -417,7 +417,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) {
raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
if (rtp->percpu_enqueue_lim > 1) {
- WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids) + 1);
+ WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids));
smp_store_release(&rtp->percpu_enqueue_lim, 1);
rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu();
pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name);
--
2.31.1.189.g2e36527f23
