From 35f5cad8c4bab94ecc5acdc4055df5ea12dc76f8 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 28 Mar 2006 16:11:19 -0800 Subject: [PATCH] revert "Optimize sys_times for a single thread process" This patch reverts 'CONFIG_SMP && thread_group_empty()' optimization in sys_times(). The reason is that the next patch breaks memory ordering which is needed for that optimization. tasklist_lock in sys_times() will be eliminated completely by further patch. Signed-off-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/exit.c | 6 +---- kernel/sys.c | 86 ++++++++++++++++++----------------------------------------- 2 files changed, 27 insertions(+), 65 deletions(-) (limited to 'kernel') diff --git a/kernel/exit.c b/kernel/exit.c index 3823ec89d7b8..6b2e4cf3e140 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -139,11 +139,7 @@ repeat: ptrace_unlink(p); BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children)); __exit_signal(p); - /* - * Note that the fastpath in sys_times depends on __exit_signal having - * updated the counters before a task is removed from the tasklist of - * the process by __unhash_process. - */ + __unhash_process(p); /* diff --git a/kernel/sys.c b/kernel/sys.c index c93d37f71aef..84371fdc660b 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1202,69 +1202,35 @@ asmlinkage long sys_times(struct tms __user * tbuf) */ if (tbuf) { struct tms tmp; + struct task_struct *tsk = current; + struct task_struct *t; cputime_t utime, stime, cutime, cstime; -#ifdef CONFIG_SMP - if (thread_group_empty(current)) { - /* - * Single thread case without the use of any locks. - * - * We may race with release_task if two threads are - * executing. However, release task first adds up the - * counters (__exit_signal) before removing the task - * from the process tasklist (__unhash_process). - * __exit_signal also acquires and releases the - * siglock which results in the proper memory ordering - * so that the list modifications are always visible - * after the counters have been updated. - * - * If the counters have been updated by the second thread - * but the thread has not yet been removed from the list - * then the other branch will be executing which will - * block on tasklist_lock until the exit handling of the - * other task is finished. - * - * This also implies that the sighand->siglock cannot - * be held by another processor. So we can also - * skip acquiring that lock. - */ - utime = cputime_add(current->signal->utime, current->utime); - stime = cputime_add(current->signal->utime, current->stime); - cutime = current->signal->cutime; - cstime = current->signal->cstime; - } else -#endif - { - - /* Process with multiple threads */ - struct task_struct *tsk = current; - struct task_struct *t; - - read_lock(&tasklist_lock); - utime = tsk->signal->utime; - stime = tsk->signal->stime; - t = tsk; - do { - utime = cputime_add(utime, t->utime); - stime = cputime_add(stime, t->stime); - t = next_thread(t); - } while (t != tsk); + read_lock(&tasklist_lock); + utime = tsk->signal->utime; + stime = tsk->signal->stime; + t = tsk; + do { + utime = cputime_add(utime, t->utime); + stime = cputime_add(stime, t->stime); + t = next_thread(t); + } while (t != tsk); + + /* + * While we have tasklist_lock read-locked, no dying thread + * can be updating current->signal->[us]time. Instead, + * we got their counts included in the live thread loop. + * However, another thread can come in right now and + * do a wait call that updates current->signal->c[us]time. + * To make sure we always see that pair updated atomically, + * we take the siglock around fetching them. + */ + spin_lock_irq(&tsk->sighand->siglock); + cutime = tsk->signal->cutime; + cstime = tsk->signal->cstime; + spin_unlock_irq(&tsk->sighand->siglock); + read_unlock(&tasklist_lock); - /* - * While we have tasklist_lock read-locked, no dying thread - * can be updating current->signal->[us]time. Instead, - * we got their counts included in the live thread loop. - * However, another thread can come in right now and - * do a wait call that updates current->signal->c[us]time. - * To make sure we always see that pair updated atomically, - * we take the siglock around fetching them. - */ - spin_lock_irq(&tsk->sighand->siglock); - cutime = tsk->signal->cutime; - cstime = tsk->signal->cstime; - spin_unlock_irq(&tsk->sighand->siglock); - read_unlock(&tasklist_lock); - } tmp.tms_utime = cputime_to_clock_t(utime); tmp.tms_stime = cputime_to_clock_t(stime); tmp.tms_cutime = cputime_to_clock_t(cutime); -- cgit v1.2.2