diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcu/tree.h | 1 | ||||
| -rw-r--r-- | kernel/rcu/tree_nocb.h | 32 |
2 files changed, 6 insertions, 27 deletions
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index bae7925c497f..179f60ca0313 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -223,7 +223,6 @@ struct rcu_data { struct swait_queue_head nocb_state_wq; /* For offloading state changes */ struct task_struct *nocb_gp_kthread; raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ - atomic_t nocb_lock_contended; /* Contention experienced. */ int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ struct timer_list nocb_timer; /* Enforce finite deferral. */ unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 808c9a19fe1d..3ce30841119a 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -91,8 +91,7 @@ module_param(nocb_nobypass_lim_per_jiffy, int, 0); /* * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the - * lock isn't immediately available, increment ->nocb_lock_contended to - * flag the contention. + * lock isn't immediately available, perform minimal sanity check. */ static void rcu_nocb_bypass_lock(struct rcu_data *rdp) __acquires(&rdp->nocb_bypass_lock) @@ -100,29 +99,12 @@ static void rcu_nocb_bypass_lock(struct rcu_data *rdp) lockdep_assert_irqs_disabled(); if (raw_spin_trylock(&rdp->nocb_bypass_lock)) return; - atomic_inc(&rdp->nocb_lock_contended); + /* + * Contention expected only when local enqueue collide with + * remote flush from kthreads. + */ WARN_ON_ONCE(smp_processor_id() != rdp->cpu); - smp_mb__after_atomic(); /* atomic_inc() before lock. */ raw_spin_lock(&rdp->nocb_bypass_lock); - smp_mb__before_atomic(); /* atomic_dec() after lock. */ - atomic_dec(&rdp->nocb_lock_contended); -} - -/* - * Spinwait until the specified rcu_data structure's ->nocb_lock is - * not contended. Please note that this is extremely special-purpose, - * relying on the fact that at most two kthreads and one CPU contend for - * this lock, and also that the two kthreads are guaranteed to have frequent - * grace-period-duration time intervals between successive acquisitions - * of the lock. This allows us to use an extremely simple throttling - * mechanism, and further to apply it only to the CPU doing floods of - * call_rcu() invocations. Don't try this at home! - */ -static void rcu_nocb_wait_contended(struct rcu_data *rdp) -{ - WARN_ON_ONCE(smp_processor_id() != rdp->cpu); - while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended))) - cpu_relax(); } /* @@ -510,7 +492,6 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, } // We need to use the bypass. - rcu_nocb_wait_contended(rdp); rcu_nocb_bypass_lock(rdp); ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ @@ -1631,12 +1612,11 @@ static void show_rcu_nocb_state(struct rcu_data *rdp) sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]); sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]); - pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n", + pr_info(" CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n", rdp->cpu, rdp->nocb_gp_rdp->cpu, nocb_next_rdp ? nocb_next_rdp->cpu : -1, "kK"[!!rdp->nocb_cb_kthread], "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)], - "cC"[!!atomic_read(&rdp->nocb_lock_contended)], "lL"[raw_spin_is_locked(&rdp->nocb_lock)], "sS"[!!rdp->nocb_cb_sleep], ".W"[swait_active(&rdp->nocb_cb_wq)], |