diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-01-30 17:23:19 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-03-31 13:34:07 -0700 |
| commit | e2fd9d35847d1936398d44c4df68dceb3d7f64e7 (patch) | |
| tree | 1893e200e6f5e87065b38fedfc9f74d19a4079b7 /kernel/rcu | |
| parent | 4f41530245c7fd4837152e264d120d05ae940eb0 (diff) | |
rcu: Remove expedited GP funnel-lock bypass
Commit #cdacbe1f91264 ("rcu: Add fastpath bypassing funnel locking")
turns out to be a pessimization at high load because it forces a tree
full of tasks to wait for an expedited grace period that they probably
do not need. This commit therefore removes this optimization.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 19 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 1 | ||||
| -rw-r--r-- | kernel/rcu/tree_trace.c | 7 |
3 files changed, 3 insertions, 24 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 524026fd9dd7..62e73e0a929f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3617,25 +3617,6 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s) struct rcu_node *rnp1 = NULL; /* - * First try directly acquiring the root lock in order to reduce - * latency in the common case where expedited grace periods are - * rare. We check mutex_is_locked() to avoid pathological levels of - * memory contention on ->exp_funnel_mutex in the heavy-load case. - */ - rnp0 = rcu_get_root(rsp); - if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) { - if (mutex_trylock(&rnp0->exp_funnel_mutex)) { - trace_rcu_exp_funnel_lock(rsp->name, rnp0->level, - rnp0->grplo, rnp0->grphi, - TPS("acq")); - if (sync_exp_work_done(rsp, rnp0, NULL, - &rdp->expedited_workdone0, s)) - return NULL; - return rnp0; - } - } - - /* * Each pass through the following loop works its way * up the rcu_node tree, returning if others have done the * work or otherwise falls through holding the root rnp's diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index df668c0f9e64..ac9a7b0c36ae 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -388,7 +388,6 @@ struct rcu_data { struct rcu_head oom_head; #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ struct mutex exp_funnel_mutex; - atomic_long_t expedited_workdone0; /* # done by others #0. */ atomic_long_t expedited_workdone1; /* # done by others #1. */ atomic_long_t expedited_workdone2; /* # done by others #2. */ atomic_long_t expedited_workdone3; /* # done by others #3. */ diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index 1088e64f01ad..d149c412a4e5 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -185,17 +185,16 @@ static int show_rcuexp(struct seq_file *m, void *v) int cpu; struct rcu_state *rsp = (struct rcu_state *)m->private; struct rcu_data *rdp; - unsigned long s0 = 0, s1 = 0, s2 = 0, s3 = 0; + unsigned long s1 = 0, s2 = 0, s3 = 0; for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(rsp->rda, cpu); - s0 += atomic_long_read(&rdp->expedited_workdone0); s1 += atomic_long_read(&rdp->expedited_workdone1); s2 += atomic_long_read(&rdp->expedited_workdone2); s3 += atomic_long_read(&rdp->expedited_workdone3); } - seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", - rsp->expedited_sequence, s0, s1, s2, s3, + seq_printf(m, "s=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", + rsp->expedited_sequence, s1, s2, s3, atomic_long_read(&rsp->expedited_normal), atomic_read(&rsp->expedited_need_qs), rsp->expedited_sequence / 2); |