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| author | Paul E. McKenney <paulmck@kernel.org> | 2022-02-02 15:42:36 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-02-08 10:13:12 -0800 |
| commit | 2bcd18e041fc3c2ae58f41eb5e18790c7c82c674 (patch) | |
| tree | 22b3902e5c6535584432304cb9d20dafe27853f9 /kernel/rcu | |
| parent | da123016ca8cb5697366c0b2dd55059b976e67e4 (diff) | |
| download | linux-stable-2bcd18e041fc3c2ae58f41eb5e18790c7c82c674.tar.gz linux-stable-2bcd18e041fc3c2ae58f41eb5e18790c7c82c674.tar.bz2 linux-stable-2bcd18e041fc3c2ae58f41eb5e18790c7c82c674.zip | |
rcu-tasks: Use order_base_2() instead of ilog2()
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@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tasks.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index d64f0b1d8cd3..670c75cbcb98 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); |