1 files changed, 323 insertions, 0 deletions

diff --git a/kernel/async.c b/kernel/async.c
new file mode 100644
index 000000000000..64cc916299a5
--- /dev/null
+++ b/kernel/async.c
@@ -0,0 +1,323 @@
+/*
+ * 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/module.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/kthread.h>
+#include <asm/atomic.h>
+
+static async_cookie_t next_cookie = 1;
+
+#define MAX_THREADS     256
+#define MAX_WORK        32768
+
+static LIST_HEAD(async_pending);
+static LIST_HEAD(async_running);
+static DEFINE_SPINLOCK(async_lock);
+
+struct async_entry {
+        struct list_head list;
+        async_cookie_t   cookie;
+        async_func_ptr   *func;
+        void             *data;
+        struct list_head *running;
+};
+
+static DECLARE_WAIT_QUEUE_HEAD(async_done);
+static DECLARE_WAIT_QUEUE_HEAD(async_new);
+
+static atomic_t entry_count;
+static atomic_t thread_count;
+
+extern int initcall_debug;
+
+
+/*
+ * MUST be called with the lock held!
+ */
+static async_cookie_t  __lowest_in_progress(struct list_head *running)
+{
+        struct async_entry *entry;
+        if (!list_empty(&async_pending)) {
+                entry = list_first_entry(&async_pending,
+                        struct async_entry, list);
+                return entry->cookie;
+        } else if (!list_empty(running)) {
+                entry = list_first_entry(running,
+                        struct async_entry, list);
+                return entry->cookie;
+        } else {
+                /* nothing in progress... next_cookie is "infinity" */
+                return next_cookie;
+        }
+
+}
+/*
+ * pick the first pending entry and run it
+ */
+static void run_one_entry(void)
+{
+        unsigned long flags;
+        struct async_entry *entry;
+        ktime_t calltime, delta, rettime;
+
+        /* 1) pick one task from the pending queue */
+
+        spin_lock_irqsave(&async_lock, flags);
+        if (list_empty(&async_pending))
+                goto out;
+        entry = list_first_entry(&async_pending, struct async_entry, list);
+
+        /* 2) move it to the running queue */
+        list_del(&entry->list);
+        list_add_tail(&entry->list, &async_running);
+        spin_unlock_irqrestore(&async_lock, flags);
+
+        /* 3) run it (and print duration)*/
+        if (initcall_debug && system_state == SYSTEM_BOOTING) {
+                printk("calling  %lli_%pF @ %i\n", 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);
+                printk("initcall %lli_%pF returned 0 after %lld usecs\n", entry->cookie,
+                        entry->func, ktime_to_ns(delta) >> 10);
+        }
+
+        /* 4) remove it from the running queue */
+        spin_lock_irqsave(&async_lock, flags);
+        list_del(&entry->list);
+
+        /* 5) free the entry  */
+        kfree(entry);
+        atomic_dec(&entry_count);
+
+        spin_unlock_irqrestore(&async_lock, flags);
+
+        /* 6) wake up any waiters. */
+        wake_up(&async_done);
+        return;
+
+out:
+        spin_unlock_irqrestore(&async_lock, flags);
+}
+
+
+static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
+{
+        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 */
+                ptr(data, newcookie);
+                return newcookie;
+        }
+        entry->func = ptr;
+        entry->data = data;
+        entry->running = running;
+
+        spin_lock_irqsave(&async_lock, flags);
+        newcookie = entry->cookie = next_cookie++;
+        list_add_tail(&entry->list, &async_pending);
+        atomic_inc(&entry_count);
+        spin_unlock_irqrestore(&async_lock, flags);
+        wake_up(&async_new);
+        return newcookie;
+}
+
+async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
+{
+        return __async_schedule(ptr, data, &async_pending);
+}
+EXPORT_SYMBOL_GPL(async_schedule);
+
+async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running)
+{
+        return __async_schedule(ptr, data, running);
+}
+EXPORT_SYMBOL_GPL(async_schedule_special);
+
+void async_synchronize_full(void)
+{
+        do {
+                async_synchronize_cookie(next_cookie);
+        } while (!list_empty(&async_running) || !list_empty(&async_pending));
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full);
+
+void async_synchronize_full_special(struct list_head *list)
+{
+        async_synchronize_cookie_special(next_cookie, list);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full_special);
+
+void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running)
+{
+        ktime_t starttime, delta, endtime;
+
+        if (initcall_debug && system_state == SYSTEM_BOOTING) {
+                printk("async_waiting @ %i\n", task_pid_nr(current));
+                starttime = ktime_get();
+        }
+
+        wait_event(async_done, __lowest_in_progress(running) >= cookie);
+
+        if (initcall_debug && system_state == SYSTEM_BOOTING) {
+                endtime = ktime_get();
+                delta = ktime_sub(endtime, starttime);
+
+                printk("async_continuing @ %i after %lli usec\n",
+                        task_pid_nr(current), ktime_to_ns(delta) >> 10);
+        }
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie_special);
+
+void async_synchronize_cookie(async_cookie_t cookie)
+{
+        async_synchronize_cookie_special(cookie, &async_running);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie);
+
+
+static int async_thread(void *unused)
+{
+        DECLARE_WAITQUEUE(wq, current);
+        add_wait_queue(&async_new, &wq);
+
+        while (!kthread_should_stop()) {
+                int ret = HZ;
+                set_current_state(TASK_INTERRUPTIBLE);
+                /*
+                 * check the list head without lock.. false positives
+                 * are dealt with inside run_one_entry() while holding
+                 * the lock.
+                 */
+                rmb();
+                if (!list_empty(&async_pending))
+                        run_one_entry();
+                else
+                        ret = schedule_timeout(HZ);
+
+                if (ret == 0) {
+                        /*
+                         * we timed out, this means we as thread are redundant.
+                         * we sign off and die, but we to avoid any races there
+                         * is a last-straw check to see if work snuck in.
+                         */
+                        atomic_dec(&thread_count);
+                        wmb(); /* manager must see our departure first */
+                        if (list_empty(&async_pending))
+                                break;
+                        /*
+                         * woops work came in between us timing out and us
+                         * signing off; we need to stay alive and keep working.
+                         */
+                        atomic_inc(&thread_count);
+                }
+        }
+        remove_wait_queue(&async_new, &wq);
+
+        return 0;
+}
+
+static int async_manager_thread(void *unused)
+{
+        DECLARE_WAITQUEUE(wq, current);
+        add_wait_queue(&async_new, &wq);
+
+        while (!kthread_should_stop()) {
+                int tc, ec;
+
+                set_current_state(TASK_INTERRUPTIBLE);
+
+                tc = atomic_read(&thread_count);
+                rmb();
+                ec = atomic_read(&entry_count);
+
+                while (tc < ec && tc < MAX_THREADS) {
+                        kthread_run(async_thread, NULL, "async/%i", tc);
+                        atomic_inc(&thread_count);
+                        tc++;
+                }
+
+                schedule();
+        }
+        remove_wait_queue(&async_new, &wq);
+
+        return 0;
+}
+
+static int __init async_init(void)
+{
+        kthread_run(async_manager_thread, NULL, "async/mgr");
+        return 0;
+}
+
+core_initcall(async_init);