The following commit has been merged into the core/rcu branch of tip: Commit-ID: b864f89ff61492f56b4e8c6713a5efec6540a0e2 Gitweb: https://git.kernel.org/tip/b864f89ff61492f56b4e8c6713a5efec6540a0e2 Author: Paul E. McKenney <[email protected]> AuthorDate: Tue, 26 May 2020 10:57:34 -07:00 Committer: Paul E. McKenney <[email protected]> CommitterDate: Mon, 29 Jun 2020 12:00:45 -07:00
refperf: Tune reader measurement interval This commit moves a printk() out of the measurement interval, converts a atomic_dec()/atomic_read() pair to atomic_dec_and_test(), and adds a smp_mb__before_atomic() to avoid potential wake/wait hangs. These changes have the added benefit of reducing the number of loops required for amortizing loop overhead for CONFIG_PREEMPT=n RCU measurements from 1,000,000 to 10,000. This reduction in turn shortens the test, reducing the probability of interference. Cc: Joel Fernandes (Google) <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/refperf.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c index 0a900f3..8815ccf 100644 --- a/kernel/rcu/refperf.c +++ b/kernel/rcu/refperf.c @@ -252,15 +252,16 @@ repeat: // Make sure that the CPU is affinitized appropriately during testing. WARN_ON_ONCE(smp_processor_id() != me); + smp_mb__before_atomic(); atomic_dec(&rt->start); + VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx); + // To prevent noise, keep interrupts disabled. This also has the // effect of preventing entries into slow path for rcu_read_unlock(). local_irq_save(flags); start = ktime_get_mono_fast_ns(); - VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx); - cur_ops->readsection(loops); duration = ktime_get_mono_fast_ns() - start; @@ -268,14 +269,12 @@ repeat: rt->last_duration_ns = WARN_ON_ONCE(duration < 0) ? 0 : duration; - atomic_dec(&nreaders_exp); + if (atomic_dec_and_test(&nreaders_exp)) + wake_up(&main_wq); VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d ended, (readers remaining=%d)", me, exp_idx, atomic_read(&nreaders_exp)); - if (!atomic_read(&nreaders_exp)) - wake_up(&main_wq); - if (!torture_must_stop()) goto repeat; end:
