diff options
| -rw-r--r-- | kernel/rcutiny_plugin.h | 163 |
1 files changed, 89 insertions, 74 deletions
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 2b8d5293c5f4..f259c676195f 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -106,15 +106,22 @@ struct rcu_preempt_ctrlblk { unsigned long n_grace_periods; #ifdef CONFIG_RCU_BOOST unsigned long n_tasks_boosted; + /* Total number of tasks boosted. */ unsigned long n_exp_boosts; + /* Number of tasks boosted for expedited GP. */ unsigned long n_normal_boosts; - unsigned long n_normal_balk_blkd_tasks; - unsigned long n_normal_balk_gp_tasks; - unsigned long n_normal_balk_boost_tasks; - unsigned long n_normal_balk_notyet; - unsigned long n_normal_balk_nos; - unsigned long n_exp_balk_blkd_tasks; - unsigned long n_exp_balk_nos; + /* Number of tasks boosted for normal GP. */ + unsigned long n_balk_blkd_tasks; + /* Refused to boost: no blocked tasks. */ + unsigned long n_balk_exp_gp_tasks; + /* Refused to boost: nothing blocking GP. */ + unsigned long n_balk_boost_tasks; + /* Refused to boost: already boosting. */ + unsigned long n_balk_notyet; + /* Refused to boost: not yet time. */ + unsigned long n_balk_nos; + /* Refused to boost: not sure why, though. */ + /* This can happen due to race conditions. */ #endif /* #ifdef CONFIG_RCU_BOOST */ #endif /* #ifdef CONFIG_RCU_TRACE */ }; @@ -199,7 +206,6 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t) #ifdef CONFIG_RCU_BOOST static void rcu_initiate_boost_trace(void); -static void rcu_initiate_exp_boost_trace(void); #endif /* #ifdef CONFIG_RCU_BOOST */ /* @@ -225,16 +231,13 @@ static void show_tiny_preempt_stats(struct seq_file *m) rcu_preempt_ctrlblk.n_normal_boosts, (int)(jiffies & 0xffff), (int)(rcu_preempt_ctrlblk.boost_time & 0xffff)); - seq_printf(m, " %s: nt=%lu gt=%lu bt=%lu ny=%lu nos=%lu\n", - "normal balk", - rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks, - rcu_preempt_ctrlblk.n_normal_balk_gp_tasks, - rcu_preempt_ctrlblk.n_normal_balk_boost_tasks, - rcu_preempt_ctrlblk.n_normal_balk_notyet, - rcu_preempt_ctrlblk.n_normal_balk_nos); - seq_printf(m, " exp balk: bt=%lu nos=%lu\n", - rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks, - rcu_preempt_ctrlblk.n_exp_balk_nos); + seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n", + " balk", + rcu_preempt_ctrlblk.n_balk_blkd_tasks, + rcu_preempt_ctrlblk.n_balk_exp_gp_tasks, + rcu_preempt_ctrlblk.n_balk_boost_tasks, + rcu_preempt_ctrlblk.n_balk_notyet, + rcu_preempt_ctrlblk.n_balk_nos); #endif /* #ifdef CONFIG_RCU_BOOST */ } @@ -252,23 +255,59 @@ static int rcu_boost(void) { unsigned long flags; struct rt_mutex mtx; - struct list_head *np; struct task_struct *t; + struct list_head *tb; - if (rcu_preempt_ctrlblk.boost_tasks == NULL) + if (rcu_preempt_ctrlblk.boost_tasks == NULL && + rcu_preempt_ctrlblk.exp_tasks == NULL) return 0; /* Nothing to boost. */ + raw_local_irq_save(flags); - t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct, - rcu_node_entry); - np = rcu_next_node_entry(t); + + /* + * Recheck with irqs disabled: all tasks in need of boosting + * might exit their RCU read-side critical sections on their own + * if we are preempted just before disabling irqs. + */ + if (rcu_preempt_ctrlblk.boost_tasks == NULL && + rcu_preempt_ctrlblk.exp_tasks == NULL) { + raw_local_irq_restore(flags); + return 0; + } + + /* + * Preferentially boost tasks blocking expedited grace periods. + * This cannot starve the normal grace periods because a second + * expedited grace period must boost all blocked tasks, including + * those blocking the pre-existing normal grace period. + */ + if (rcu_preempt_ctrlblk.exp_tasks != NULL) { + tb = rcu_preempt_ctrlblk.exp_tasks; + RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); + } else { + tb = rcu_preempt_ctrlblk.boost_tasks; + RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); + } + RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); + + /* + * We boost task t by manufacturing an rt_mutex that appears to + * be held by task t. We leave a pointer to that rt_mutex where + * task t can find it, and task t will release the mutex when it + * exits its outermost RCU read-side critical section. Then + * simply acquiring this artificial rt_mutex will boost task + * t's priority. (Thanks to tglx for suggesting this approach!) + */ + t = container_of(tb, struct task_struct, rcu_node_entry); rt_mutex_init_proxy_locked(&mtx, t); t->rcu_boost_mutex = &mtx; t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; raw_local_irq_restore(flags); rt_mutex_lock(&mtx); - RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); - rt_mutex_unlock(&mtx); - return rcu_preempt_ctrlblk.boost_tasks != NULL; + rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ + + return rcu_preempt_ctrlblk.boost_tasks != NULL || + rcu_preempt_ctrlblk.exp_tasks != NULL; } /* @@ -283,39 +322,24 @@ static int rcu_boost(void) */ static int rcu_initiate_boost(void) { - if (!rcu_preempt_blocked_readers_cgp()) { - RCU_TRACE(rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks++); + if (!rcu_preempt_blocked_readers_cgp() && + rcu_preempt_ctrlblk.exp_tasks == NULL) { + RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++); return 0; } - if (rcu_preempt_ctrlblk.gp_tasks != NULL && - rcu_preempt_ctrlblk.boost_tasks == NULL && - ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) { - rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks; + if (rcu_preempt_ctrlblk.exp_tasks != NULL || + (rcu_preempt_ctrlblk.gp_tasks != NULL && + rcu_preempt_ctrlblk.boost_tasks == NULL && + ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) { + if (rcu_preempt_ctrlblk.exp_tasks == NULL) + rcu_preempt_ctrlblk.boost_tasks = + rcu_preempt_ctrlblk.gp_tasks; invoke_rcu_kthread(); - RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); } else RCU_TRACE(rcu_initiate_boost_trace()); return 1; } -/* - * Initiate boosting for an expedited grace period. - */ -static void rcu_initiate_expedited_boost(void) -{ - unsigned long flags; - - raw_local_irq_save(flags); - if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) { - rcu_preempt_ctrlblk.boost_tasks = - rcu_preempt_ctrlblk.blkd_tasks.next; - invoke_rcu_kthread(); - RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); - } else - RCU_TRACE(rcu_initiate_exp_boost_trace()); - raw_local_irq_restore(flags); -} - #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) /* @@ -347,13 +371,6 @@ static int rcu_initiate_boost(void) } /* - * If there is no RCU priority boosting, we don't initiate expedited boosting. - */ -static void rcu_initiate_expedited_boost(void) -{ -} - -/* * If there is no RCU priority boosting, nothing to do at grace-period start. */ static void rcu_preempt_boost_start_gp(void) @@ -786,13 +803,16 @@ void synchronize_rcu_expedited(void) rpcp->exp_tasks = rpcp->blkd_tasks.next; if (rpcp->exp_tasks == &rpcp->blkd_tasks) rpcp->exp_tasks = NULL; - local_irq_restore(flags); /* Wait for tail of ->blkd_tasks list to drain. */ - if (rcu_preempted_readers_exp()) - rcu_initiate_expedited_boost(); + if (!rcu_preempted_readers_exp()) + local_irq_restore(flags); + else { + rcu_initiate_boost(); + local_irq_restore(flags); wait_event(sync_rcu_preempt_exp_wq, !rcu_preempted_readers_exp()); + } /* Clean up and exit. */ barrier(); /* ensure expedited GP seen before counter increment. */ @@ -905,22 +925,17 @@ void __init rcu_scheduler_starting(void) static void rcu_initiate_boost_trace(void) { - if (rcu_preempt_ctrlblk.gp_tasks == NULL) - rcu_preempt_ctrlblk.n_normal_balk_gp_tasks++; + if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) + rcu_preempt_ctrlblk.n_balk_blkd_tasks++; + else if (rcu_preempt_ctrlblk.gp_tasks == NULL && + rcu_preempt_ctrlblk.exp_tasks == NULL) + rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++; else if (rcu_preempt_ctrlblk.boost_tasks != NULL) - rcu_preempt_ctrlblk.n_normal_balk_boost_tasks++; + rcu_preempt_ctrlblk.n_balk_boost_tasks++; else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) - rcu_preempt_ctrlblk.n_normal_balk_notyet++; - else - rcu_preempt_ctrlblk.n_normal_balk_nos++; -} - -static void rcu_initiate_exp_boost_trace(void) -{ - if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) - rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks++; + rcu_preempt_ctrlblk.n_balk_notyet++; else - rcu_preempt_ctrlblk.n_exp_balk_nos++; + rcu_preempt_ctrlblk.n_balk_nos++; } #endif /* #ifdef CONFIG_RCU_BOOST */ |