litmus-rt.git - The LITMUS^RT kernel.

diff options

Diffstat (limited to 'kernel/trace/trace.c')

0 files changed, 0 insertions, 0 deletions

/* * 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_RUNNING) { 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_RUNNING) { 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


context:
space:
mode: