diff options
Diffstat (limited to 'kernel/rcutree_plugin.h')
| -rw-r--r-- | kernel/rcutree_plugin.h | 415 |
1 files changed, 409 insertions, 6 deletions
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index f92115488187..f6e5ec2932b4 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,6 +25,7 @@ */ #include <linux/delay.h> +#include <linux/gfp.h> #include <linux/oom.h> #include <linux/smpboot.h> @@ -36,6 +37,14 @@ #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO #endif +#ifdef CONFIG_RCU_NOCB_CPU +static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ +static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ +static bool rcu_nocb_poll; /* Offload kthread are to poll. */ +module_param(rcu_nocb_poll, bool, 0444); +static char __initdata nocb_buf[NR_CPUS * 5]; +#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ + /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary. If you like #ifdef, you @@ -76,6 +85,18 @@ static void __init rcu_bootup_announce_oddness(void) printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); if (nr_cpu_ids != NR_CPUS) printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); +#ifdef CONFIG_RCU_NOCB_CPU + if (have_rcu_nocb_mask) { + if (cpumask_test_cpu(0, rcu_nocb_mask)) { + cpumask_clear_cpu(0, rcu_nocb_mask); + pr_info("\tCPU 0: illegal no-CBs CPU (cleared).\n"); + } + cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); + pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf); + if (rcu_nocb_poll) + pr_info("\tExperimental polled no-CBs CPUs.\n"); + } +#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ } #ifdef CONFIG_TREE_PREEMPT_RCU @@ -642,7 +663,7 @@ static void rcu_preempt_do_callbacks(void) */ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_preempt_state, 0); + __call_rcu(head, func, &rcu_preempt_state, -1, 0); } EXPORT_SYMBOL_GPL(call_rcu); @@ -656,7 +677,7 @@ EXPORT_SYMBOL_GPL(call_rcu); void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_preempt_state, 1); + __call_rcu(head, func, &rcu_preempt_state, -1, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu); @@ -670,6 +691,9 @@ EXPORT_SYMBOL_GPL(kfree_call_rcu); * concurrently with new RCU read-side critical sections that began while * synchronize_rcu() was waiting. RCU read-side critical sections are * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. + * + * See the description of synchronize_sched() for more detailed information + * on memory ordering guarantees. */ void synchronize_rcu(void) { @@ -679,7 +703,10 @@ void synchronize_rcu(void) "Illegal synchronize_rcu() in RCU read-side critical section"); if (!rcu_scheduler_active) return; - wait_rcu_gp(call_rcu); + if (rcu_expedited) + synchronize_rcu_expedited(); + else + wait_rcu_gp(call_rcu); } EXPORT_SYMBOL_GPL(synchronize_rcu); @@ -757,7 +784,8 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, * grace period for the specified rcu_node structure. If there are no such * tasks, report it up the rcu_node hierarchy. * - * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. + * Caller must hold sync_rcu_preempt_exp_mutex and must exclude + * CPU hotplug operations. */ static void sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) @@ -831,7 +859,7 @@ void synchronize_rcu_expedited(void) udelay(trycount * num_online_cpus()); } else { put_online_cpus(); - synchronize_rcu(); + wait_rcu_gp(call_rcu); return; } } @@ -875,6 +903,11 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); /** * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. + * + * Note that this primitive does not necessarily wait for an RCU grace period + * to complete. For example, if there are no RCU callbacks queued anywhere + * in the system, then rcu_barrier() is within its rights to return + * immediately, without waiting for anything, much less an RCU grace period. */ void rcu_barrier(void) { @@ -1013,7 +1046,7 @@ static void rcu_preempt_check_callbacks(int cpu) void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { - __call_rcu(head, func, &rcu_sched_state, 1); + __call_rcu(head, func, &rcu_sched_state, -1, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu); @@ -2092,3 +2125,373 @@ static void increment_cpu_stall_ticks(void) } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ + +#ifdef CONFIG_RCU_NOCB_CPU + +/* + * Offload callback processing from the boot-time-specified set of CPUs + * specified by rcu_nocb_mask. For each CPU in the set, there is a + * kthread created that pulls the callbacks from the corresponding CPU, + * waits for a grace period to elapse, and invokes the callbacks. + * The no-CBs CPUs do a wake_up() on their kthread when they insert + * a callback into any empty list, unless the rcu_nocb_poll boot parameter + * has been specified, in which case each kthread actively polls its + * CPU. (Which isn't so great for energy efficiency, but which does + * reduce RCU's overhead on that CPU.) + * + * This is intended to be used in conjunction with Frederic Weisbecker's + * adaptive-idle work, which would seriously reduce OS jitter on CPUs + * running CPU-bound user-mode computations. + * + * Offloading of callback processing could also in theory be used as + * an energy-efficiency measure because CPUs with no RCU callbacks + * queued are more aggressive about entering dyntick-idle mode. + */ + + +/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ +static int __init rcu_nocb_setup(char *str) +{ + alloc_bootmem_cpumask_var(&rcu_nocb_mask); + have_rcu_nocb_mask = true; + cpulist_parse(str, rcu_nocb_mask); + return 1; +} +__setup("rcu_nocbs=", rcu_nocb_setup); + +/* Is the specified CPU a no-CPUs CPU? */ +static bool is_nocb_cpu(int cpu) +{ + if (have_rcu_nocb_mask) + return cpumask_test_cpu(cpu, rcu_nocb_mask); + return false; +} + +/* + * Enqueue the specified string of rcu_head structures onto the specified + * CPU's no-CBs lists. The CPU is specified by rdp, the head of the + * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy + * counts are supplied by rhcount and rhcount_lazy. + * + * If warranted, also wake up the kthread servicing this CPUs queues. + */ +static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, + struct rcu_head *rhp, + struct rcu_head **rhtp, + int rhcount, int rhcount_lazy) +{ + int len; + struct rcu_head **old_rhpp; + struct task_struct *t; + + /* Enqueue the callback on the nocb list and update counts. */ + old_rhpp = xchg(&rdp->nocb_tail, rhtp); + ACCESS_ONCE(*old_rhpp) = rhp; + atomic_long_add(rhcount, &rdp->nocb_q_count); + atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); + + /* If we are not being polled and there is a kthread, awaken it ... */ + t = ACCESS_ONCE(rdp->nocb_kthread); + if (rcu_nocb_poll | !t) + return; + len = atomic_long_read(&rdp->nocb_q_count); + if (old_rhpp == &rdp->nocb_head) { + wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */ + rdp->qlen_last_fqs_check = 0; + } else if (len > rdp->qlen_last_fqs_check + qhimark) { + wake_up_process(t); /* ... or if many callbacks queued. */ + rdp->qlen_last_fqs_check = LONG_MAX / 2; + } + return; +} + +/* + * This is a helper for __call_rcu(), which invokes this when the normal + * callback queue is inoperable. If this is not a no-CBs CPU, this + * function returns failure back to __call_rcu(), which can complain + * appropriately. + * + * Otherwise, this function queues the callback where the corresponding + * "rcuo" kthread can find it. + */ +static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, + bool lazy) +{ + + if (!is_nocb_cpu(rdp->cpu)) + return 0; + __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy); + return 1; +} + +/* + * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is + * not a no-CBs CPU. + */ +static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, + struct rcu_data *rdp) +{ + long ql = rsp->qlen; + long qll = rsp->qlen_lazy; + + /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ + if (!is_nocb_cpu(smp_processor_id())) + return 0; + rsp->qlen = 0; + rsp->qlen_lazy = 0; + + /* First, enqueue the donelist, if any. This preserves CB ordering. */ + if (rsp->orphan_donelist != NULL) { + __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, + rsp->orphan_donetail, ql, qll); + ql = qll = 0; + rsp->orphan_donelist = NULL; + rsp->orphan_donetail = &rsp->orphan_donelist; + } + if (rsp->orphan_nxtlist != NULL) { + __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, + rsp->orphan_nxttail, ql, qll); + ql = qll = 0; + rsp->orphan_nxtlist = NULL; + rsp->orphan_nxttail = &rsp->orphan_nxtlist; + } + return 1; +} + +/* + * There must be at least one non-no-CBs CPU in operation at any given + * time, because no-CBs CPUs are not capable of initiating grace periods + * independently. This function therefore complains if the specified + * CPU is the last non-no-CBs CPU, allowing the CPU-hotplug system to + * avoid offlining the last such CPU. (Recursion is a wonderful thing, + * but you have to have a base case!) + */ +static bool nocb_cpu_expendable(int cpu) +{ + cpumask_var_t non_nocb_cpus; + int ret; + + /* + * If there are no no-CB CPUs or if this CPU is not a no-CB CPU, + * then offlining this CPU is harmless. Let it happen. + */ + if (!have_rcu_nocb_mask || is_nocb_cpu(cpu)) + return 1; + + /* If no memory, play it safe and keep the CPU around. */ + if (!alloc_cpumask_var(&non_nocb_cpus, GFP_NOIO)) + return 0; + cpumask_andnot(non_nocb_cpus, cpu_online_mask, rcu_nocb_mask); + cpumask_clear_cpu(cpu, non_nocb_cpus); + ret = !cpumask_empty(non_nocb_cpus); + free_cpumask_var(non_nocb_cpus); + return ret; +} + +/* + * Helper structure for remote registry of RCU callbacks. + * This is needed for when a no-CBs CPU needs to start a grace period. + * If it just invokes call_rcu(), the resulting callback will be queued, + * which can result in deadlock. + */ +struct rcu_head_remote { + struct rcu_head *rhp; + call_rcu_func_t *crf; + void (*func)(struct rcu_head *rhp); +}; + +/* + * Register a callback as specified by the rcu_head_remote struct. + * This function is intended to be invoked via smp_call_function_single(). + */ +static void call_rcu_local(void *arg) +{ + struct rcu_head_remote *rhrp = + container_of(arg, struct rcu_head_remote, rhp); + + rhrp->crf(rhrp->rhp, rhrp->func); +} + +/* + * Set up an rcu_head_remote structure and the invoke call_rcu_local() + * on CPU 0 (which is guaranteed to be a non-no-CBs CPU) via + * smp_call_function_single(). + */ +static void invoke_crf_remote(struct rcu_head *rhp, + void (*func)(struct rcu_head *rhp), + call_rcu_func_t crf) +{ + struct rcu_head_remote rhr; + + rhr.rhp = rhp; + rhr.crf = crf; + rhr.func = func; + smp_call_function_single(0, call_rcu_local, &rhr, 1); +} + +/* + * Helper functions to be passed to wait_rcu_gp(), each of which + * invokes invoke_crf_remote() to register a callback appropriately. + */ +static void __maybe_unused +call_rcu_preempt_remote(struct rcu_head *rhp, + void (*func)(struct rcu_head *rhp)) +{ + invoke_crf_remote(rhp, func, call_rcu); +} +static void call_rcu_bh_remote(struct rcu_head *rhp, + void (*func)(struct rcu_head *rhp)) +{ + invoke_crf_remote(rhp, func, call_rcu_bh); +} +static void call_rcu_sched_remote(struct rcu_head *rhp, + void (*func)(struct rcu_head *rhp)) +{ + invoke_crf_remote(rhp, func, call_rcu_sched); +} + +/* + * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes + * callbacks queued by the corresponding no-CBs CPU. + */ +static int rcu_nocb_kthread(void *arg) +{ + int c, cl; + struct rcu_head *list; + struct rcu_head *next; + struct rcu_head **tail; + struct rcu_data *rdp = arg; + + /* Each pass through this loop invokes one batch of callbacks */ + for (;;) { + /* If not polling, wait for next batch of callbacks. */ + if (!rcu_nocb_poll) + wait_event(rdp->nocb_wq, rdp->nocb_head); + list = ACCESS_ONCE(rdp->nocb_head); + if (!list) { + schedule_timeout_interruptible(1); + continue; + } + + /* + * Extract queued callbacks, update counts, and wait + * for a grace period to elapse. + */ + ACCESS_ONCE(rdp->nocb_head) = NULL; + tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); + c = atomic_long_xchg(&rdp->nocb_q_count, 0); + cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); + ACCESS_ONCE(rdp->nocb_p_count) += c; + ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; + wait_rcu_gp(rdp->rsp->call_remote); + + /* Each pass through the following loop invokes a callback. */ + trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); + c = cl = 0; + while (list) { + next = list->next; + /* Wait for enqueuing to complete, if needed. */ + while (next == NULL && &list->next != tail) { + schedule_timeout_interruptible(1); + next = list->next; + } + debug_rcu_head_unqueue(list); + local_bh_disable(); + if (__rcu_reclaim(rdp->rsp->name, list)) + cl++; + c++; + local_bh_enable(); + list = next; + } + trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); + ACCESS_ONCE(rdp->nocb_p_count) -= c; + ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; + rdp->n_nocbs_invoked += c; + } + return 0; +} + +/* Initialize per-rcu_data variables for no-CBs CPUs. */ +static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) +{ + rdp->nocb_tail = &rdp->nocb_head; + init_waitqueue_head(&rdp->nocb_wq); +} + +/* Create a kthread for each RCU flavor for each no-CBs CPU. */ +static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) +{ + int cpu; + struct rcu_data *rdp; + struct task_struct *t; + + if (rcu_nocb_mask == NULL) + return; + for_each_cpu(cpu, rcu_nocb_mask) { + rdp = per_cpu_ptr(rsp->rda, cpu); + t = kthread_run(rcu_nocb_kthread, rdp, "rcuo%d", cpu); + BUG_ON(IS_ERR(t)); + ACCESS_ONCE(rdp->nocb_kthread) = t; + } +} + +/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ +static void init_nocb_callback_list(struct rcu_data *rdp) +{ + if (rcu_nocb_mask == NULL || + !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) + return; + rdp->nxttail[RCU_NEXT_TAIL] = NULL; +} + +/* Initialize the ->call_remote fields in the rcu_state structures. */ +static void __init rcu_init_nocb(void) +{ +#ifdef CONFIG_PREEMPT_RCU + rcu_preempt_state.call_remote = call_rcu_preempt_remote; +#endif /* #ifdef CONFIG_PREEMPT_RCU */ + rcu_bh_state.call_remote = call_rcu_bh_remote; + rcu_sched_state.call_remote = call_rcu_sched_remote; +} + +#else /* #ifdef CONFIG_RCU_NOCB_CPU */ + +static bool is_nocb_cpu(int cpu) +{ + return false; +} + +static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, + bool lazy) +{ + return 0; +} + +static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, + struct rcu_data *rdp) +{ + return 0; +} + +static bool nocb_cpu_expendable(int cpu) +{ + return 1; +} + +static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) +{ +} + +static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) +{ +} + +static void init_nocb_callback_list(struct rcu_data *rdp) +{ +} + +static void __init rcu_init_nocb(void) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |