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authorPaul E. McKenney <paulmck@kernel.org>2020-05-26 10:57:34 -0700
committerPaul E. McKenney <paulmck@kernel.org>2020-06-29 12:00:45 -0700
commitb864f89ff61492f56b4e8c6713a5efec6540a0e2 (patch)
treefc58c549c9878565559b223f596ac9289fdb7423 /kernel/rcu
parent2990750bceb05c3cdeae3a6d2683cbc4ae4de15e (diff)
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) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/refperf.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c
index 0a900f3ae151..8815ccfb6f98 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: