--- /dev/null
+/*
+ * async.c: Asynchronous function calls for boot performance
+ *
+ * (C) Copyright 2009 Intel Corporation
+ * Author: Arjan van de Ven <arjan@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+
+
+/*
+
+Goals and Theory of Operation
+
+The primary goal of this feature is to reduce the kernel boot time,
+by doing various independent hardware delays and discovery operations
+decoupled and not strictly serialized.
+
+More specifically, the asynchronous function call concept allows
+certain operations (primarily during system boot) to happen
+asynchronously, out of order, while these operations still
+have their externally visible parts happen sequentially and in-order.
+(not unlike how out-of-order CPUs retire their instructions in order)
+
+Key to the asynchronous function call implementation is the concept of
+a "sequence cookie" (which, although it has an abstracted type, can be
+thought of as a monotonically incrementing number).
+
+The async core will assign each scheduled event such a sequence cookie and
+pass this to the called functions.
+
+The asynchronously called function should before doing a globally visible
+operation, such as registering device numbers, call the
+async_synchronize_cookie() function and pass in its own cookie. The
+async_synchronize_cookie() function will make sure that all asynchronous
+operations that were scheduled prior to the operation corresponding with the
+cookie have completed.
+
+Subsystem/driver initialization code that scheduled asynchronous probe
+functions, but which shares global resources with other drivers/subsystems
+that do not use the asynchronous call feature, need to do a full
+synchronization with the async_synchronize_full() function, before returning
+from their init function. This is to maintain strict ordering between the
+asynchronous and synchronous parts of the kernel.
+
+*/
+
+#include <linux/async.h>
+#include <linux/atomic.h>
+#include <linux/ktime.h>
+#include <linux/export.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+
+#include "workqueue_internal.h"
+
+static async_cookie_t next_cookie = 1;
+
+#define MAX_WORK 32768
+#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
+
+static LIST_HEAD(async_global_pending); /* pending from all registered doms */
+static ASYNC_DOMAIN(async_dfl_domain);
+static DEFINE_SPINLOCK(async_lock);
+
+struct async_entry {
+ struct list_head domain_list;
+ struct list_head global_list;
+ struct work_struct work;
+ async_cookie_t cookie;
+ async_func_t func;
+ void *data;
+ struct async_domain *domain;
+};
+
+static DECLARE_WAIT_QUEUE_HEAD(async_done);
+
+static atomic_t entry_count;
+
+static async_cookie_t lowest_in_progress(struct async_domain *domain)
+{
+ struct list_head *pending;
+ async_cookie_t ret = ASYNC_COOKIE_MAX;
+ unsigned long flags;
+
+ spin_lock_irqsave(&async_lock, flags);
+
+ if (domain)
+ pending = &domain->pending;
+ else
+ pending = &async_global_pending;
+
+ if (!list_empty(pending))
+ ret = list_first_entry(pending, struct async_entry,
+ domain_list)->cookie;
+
+ spin_unlock_irqrestore(&async_lock, flags);
+ return ret;
+}
+
+/*
+ * pick the first pending entry and run it
+ */
+static void async_run_entry_fn(struct work_struct *work)
+{
+ struct async_entry *entry =
+ container_of(work, struct async_entry, work);
+ unsigned long flags;
+ ktime_t uninitialized_var(calltime), delta, rettime;
+
+ /* 1) run (and print duration) */
+ if (initcall_debug && system_state == SYSTEM_BOOTING) {
+ pr_debug("calling %lli_%pF @ %i\n",
+ (long long)entry->cookie,
+ entry->func, task_pid_nr(current));
+ calltime = ktime_get();
+ }
+ entry->func(entry->data, entry->cookie);
+ if (initcall_debug && system_state == SYSTEM_BOOTING) {
+ rettime = ktime_get();
+ delta = ktime_sub(rettime, calltime);
+ pr_debug("initcall %lli_%pF returned 0 after %lld usecs\n",
+ (long long)entry->cookie,
+ entry->func,
+ (long long)ktime_to_ns(delta) >> 10);
+ }
+
+ /* 2) remove self from the pending queues */
+ spin_lock_irqsave(&async_lock, flags);
+ list_del_init(&entry->domain_list);
+ list_del_init(&entry->global_list);
+
+ /* 3) free the entry */
+ kfree(entry);
+ atomic_dec(&entry_count);
+
+ spin_unlock_irqrestore(&async_lock, flags);
+
+ /* 4) wake up any waiters */
+ wake_up(&async_done);
+}
+
+static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)
+{
+ struct async_entry *entry;
+ unsigned long flags;
+ async_cookie_t newcookie;
+
+ /* allow irq-off callers */
+ entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
+
+ /*
+ * If we're out of memory or if there's too much work
+ * pending already, we execute synchronously.
+ */
+ if (!entry || atomic_read(&entry_count) > MAX_WORK) {
+ kfree(entry);
+ spin_lock_irqsave(&async_lock, flags);
+ newcookie = next_cookie++;
+ spin_unlock_irqrestore(&async_lock, flags);
+
+ /* low on memory.. run synchronously */
+ func(data, newcookie);
+ return newcookie;
+ }
+ INIT_LIST_HEAD(&entry->domain_list);
+ INIT_LIST_HEAD(&entry->global_list);
+ INIT_WORK(&entry->work, async_run_entry_fn);
+ entry->func = func;
+ entry->data = data;
+ entry->domain = domain;
+
+ spin_lock_irqsave(&async_lock, flags);
+
+ /* allocate cookie and queue */
+ newcookie = entry->cookie = next_cookie++;
+
+ list_add_tail(&entry->domain_list, &domain->pending);
+ if (domain->registered)
+ list_add_tail(&entry->global_list, &async_global_pending);
+
+ atomic_inc(&entry_count);
+ spin_unlock_irqrestore(&async_lock, flags);
+
+ /* mark that this task has queued an async job, used by module init */
+ current->flags |= PF_USED_ASYNC;
+
+ /* schedule for execution */
+ queue_work(system_unbound_wq, &entry->work);
+
+ return newcookie;
+}
+
+/**
+ * async_schedule - schedule a function for asynchronous execution
+ * @func: function to execute asynchronously
+ * @data: data pointer to pass to the function
+ *
+ * Returns an async_cookie_t that may be used for checkpointing later.
+ * Note: This function may be called from atomic or non-atomic contexts.
+ */
+async_cookie_t async_schedule(async_func_t func, void *data)
+{
+ return __async_schedule(func, data, &async_dfl_domain);
+}
+EXPORT_SYMBOL_GPL(async_schedule);
+
+/**
+ * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
+ * @func: function to execute asynchronously
+ * @data: data pointer to pass to the function
+ * @domain: the domain
+ *
+ * Returns an async_cookie_t that may be used for checkpointing later.
+ * @domain may be used in the async_synchronize_*_domain() functions to
+ * wait within a certain synchronization domain rather than globally. A
+ * synchronization domain is specified via @domain. Note: This function
+ * may be called from atomic or non-atomic contexts.
+ */
+async_cookie_t async_schedule_domain(async_func_t func, void *data,
+ struct async_domain *domain)
+{
+ return __async_schedule(func, data, domain);
+}
+EXPORT_SYMBOL_GPL(async_schedule_domain);
+
+/**
+ * async_synchronize_full - synchronize all asynchronous function calls
+ *
+ * This function waits until all asynchronous function calls have been done.
+ */
+void async_synchronize_full(void)
+{
+ async_synchronize_full_domain(NULL);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full);
+
+/**
+ * async_unregister_domain - ensure no more anonymous waiters on this domain
+ * @domain: idle domain to flush out of any async_synchronize_full instances
+ *
+ * async_synchronize_{cookie|full}_domain() are not flushed since callers
+ * of these routines should know the lifetime of @domain
+ *
+ * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
+ */
+void async_unregister_domain(struct async_domain *domain)
+{
+ spin_lock_irq(&async_lock);
+ WARN_ON(!domain->registered || !list_empty(&domain->pending));
+ domain->registered = 0;
+ spin_unlock_irq(&async_lock);
+}
+EXPORT_SYMBOL_GPL(async_unregister_domain);
+
+/**
+ * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
+ * @domain: the domain to synchronize
+ *
+ * This function waits until all asynchronous function calls for the
+ * synchronization domain specified by @domain have been done.
+ */
+void async_synchronize_full_domain(struct async_domain *domain)
+{
+ async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
+
+/**
+ * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
+ * @cookie: async_cookie_t to use as checkpoint
+ * @domain: the domain to synchronize (%NULL for all registered domains)
+ *
+ * This function waits until all asynchronous function calls for the
+ * synchronization domain specified by @domain submitted prior to @cookie
+ * have been done.
+ */
+void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
+{
+ ktime_t uninitialized_var(starttime), delta, endtime;
+
+ if (initcall_debug && system_state == SYSTEM_BOOTING) {
+ pr_debug("async_waiting @ %i\n", task_pid_nr(current));
+ starttime = ktime_get();
+ }
+
+ wait_event(async_done, lowest_in_progress(domain) >= cookie);
+
+ if (initcall_debug && system_state == SYSTEM_BOOTING) {
+ endtime = ktime_get();
+ delta = ktime_sub(endtime, starttime);
+
+ pr_debug("async_continuing @ %i after %lli usec\n",
+ task_pid_nr(current),
+ (long long)ktime_to_ns(delta) >> 10);
+ }
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
+
+/**
+ * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
+ * @cookie: async_cookie_t to use as checkpoint
+ *
+ * This function waits until all asynchronous function calls prior to @cookie
+ * have been done.
+ */
+void async_synchronize_cookie(async_cookie_t cookie)
+{
+ async_synchronize_cookie_domain(cookie, &async_dfl_domain);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie);
+
+/**
+ * current_is_async - is %current an async worker task?
+ *
+ * Returns %true if %current is an async worker task.
+ */
+bool current_is_async(void)
+{
+ struct worker *worker = current_wq_worker();
+
+ return worker && worker->current_func == async_run_entry_fn;
+}
Code Review / kvmfornfv.git / blobdiff