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| author |   Paul E. McKenney <paulmck@kernel.org> | 2020-05-26 10:57:34 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-06-29 12:00:45 -0700 |
| commit | b864f89ff61492f56b4e8c6713a5efec6540a0e2 (patch) | |
| tree | fc58c549c9878565559b223f596ac9289fdb7423 /kernel/rcu | |
| parent | refperf: Make functions static (diff) | |
| download | wireguard-linux-b864f89ff61492f56b4e8c6713a5efec6540a0e2.tar.xz wireguard-linux-b864f89ff61492f56b4e8c6713a5efec6540a0e2.zip | |
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.c | 11 |
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: |