The patch titled Subject: posix_timers: Remove dead task timer expiry caching has been removed from the -mm tree. Its filename was posix_timers-remove-dead-task-timer-expiry-caching.patch This patch was dropped because it was withdrawn ------------------------------------------------------ From: Frederic Weisbecker <fweisbec@xxxxxxxxx> Subject: posix_timers: Remove dead task timer expiry caching When reading a timer sample, posix_cpu_timer_get() and posix_cpu_timer_schedule() both perform a caching of the timer expiry time by converting its value from absolute to relative if the task has exited. The reason for this caching is not clear though, it could be: 1) For performance reasons: no need to calculate the delta after the task has died, its cputime won't change anymore. We can thus avoid some locking (sighand, tasklist_lock, rq->lock for task_delta_exec(), ...), and various operations to calculate the sample... 2) To keep the remaining delta for the timer available after the task has died. When it gets reaped, its sighand disappears, so accessing the process wide cputime through tsk->signal is probably not safe. Now, is the first reason really worth it? I have no idea if it is a case we really want to optimize. Considering the second reason, we return a disarmed zero'ed timer when tsk->sighand == NULL. So if this is an assumed reason, it's broken. And this case only concern process wide timers that have their group leader reaped. The posix cpu timer shouldn't even be available anymore at that time. Unless the group leader changed since we called posix_cpu_timer_create() after an exec? Anyway for now I'm sending this as an RFC because there may well be subtle things I left behind. Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: Stanislaw Gruszka <sgruszka@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/posix-cpu-timers.c | 67 +----------------------------------- 1 file changed, 2 insertions(+), 65 deletions(-) diff -puN kernel/posix-cpu-timers.c~posix_timers-remove-dead-task-timer-expiry-caching kernel/posix-cpu-timers.c --- a/kernel/posix-cpu-timers.c~posix_timers-remove-dead-task-timer-expiry-caching +++ a/kernel/posix-cpu-timers.c @@ -436,23 +436,6 @@ void posix_cpu_timers_exit_group(struct tsk->se.sum_exec_runtime + sig->sum_sched_runtime); } -static void clear_dead_task(struct k_itimer *itimer, unsigned long long now) -{ - struct cpu_timer_list *timer = &itimer->it.cpu; - - /* - * That's all for this thread or process. - * We leave our residual in expires to be reported. - */ - put_task_struct(timer->task); - timer->task = NULL; - if (timer->expires < now) { - timer->expires = 0; - } else { - timer->expires -= now; - } -} - static inline int expires_gt(cputime_t expires, cputime_t new_exp) { return expires == 0 || expires > new_exp; @@ -737,7 +720,6 @@ static void posix_cpu_timer_get(struct k { unsigned long long now; struct task_struct *p = timer->it.cpu.task; - int clear_dead; /* * Easy part: convert the reload time. @@ -750,23 +732,11 @@ static void posix_cpu_timer_get(struct k return; } - if (unlikely(p == NULL)) { - /* - * This task already died and the timer will never fire. - * In this case, expires is actually the dead value. - */ - dead: - sample_to_timespec(timer->it_clock, timer->it.cpu.expires, - &itp->it_value); - return; - } - /* * Sample the clock to take the difference with the expiry time. */ if (CPUCLOCK_PERTHREAD(timer->it_clock)) { cpu_clock_sample(timer->it_clock, p, &now); - clear_dead = p->exit_state; } else { read_lock(&tasklist_lock); if (unlikely(p->sighand == NULL)) { @@ -775,29 +745,16 @@ static void posix_cpu_timer_get(struct k * We can't even collect a sample any more. * Call the timer disarmed, nothing else to do. */ - put_task_struct(p); - timer->it.cpu.task = NULL; timer->it.cpu.expires = 0; + itp->it_value.tv_sec = itp->it_value.tv_nsec = 0; read_unlock(&tasklist_lock); - goto dead; + return; } else { cpu_timer_sample_group(timer->it_clock, p, &now); - clear_dead = (unlikely(p->exit_state) && - thread_group_empty(p)); } read_unlock(&tasklist_lock); } - if (unlikely(clear_dead)) { - /* - * We've noticed that the thread is dead, but - * not yet reaped. Take this opportunity to - * drop our task ref. - */ - clear_dead_task(timer, now); - goto dead; - } - if (now < timer->it.cpu.expires) { sample_to_timespec(timer->it_clock, timer->it.cpu.expires - now, @@ -1027,22 +984,12 @@ void posix_cpu_timer_schedule(struct k_i struct task_struct *p = timer->it.cpu.task; unsigned long long now; - if (unlikely(p == NULL)) - /* - * The task was cleaned up already, no future firings. - */ - goto out; - /* * Fetch the current sample and update the timer's expiry time. */ if (CPUCLOCK_PERTHREAD(timer->it_clock)) { cpu_clock_sample(timer->it_clock, p, &now); bump_cpu_timer(timer, now); - if (unlikely(p->exit_state)) { - clear_dead_task(timer, now); - goto out; - } read_lock(&tasklist_lock); /* arm_timer needs it. */ spin_lock(&p->sighand->siglock); } else { @@ -1056,15 +1003,6 @@ void posix_cpu_timer_schedule(struct k_i timer->it.cpu.task = p = NULL; timer->it.cpu.expires = 0; goto out_unlock; - } else if (unlikely(p->exit_state) && thread_group_empty(p)) { - /* - * We've noticed that the thread is dead, but - * not yet reaped. Take this opportunity to - * drop our task ref. - */ - cpu_timer_sample_group(timer->it_clock, p, &now); - clear_dead_task(timer, now); - goto out_unlock; } spin_lock(&p->sighand->siglock); cpu_timer_sample_group(timer->it_clock, p, &now); @@ -1082,7 +1020,6 @@ void posix_cpu_timer_schedule(struct k_i out_unlock: read_unlock(&tasklist_lock); -out: timer->it_overrun_last = timer->it_overrun; timer->it_overrun = -1; ++timer->it_requeue_pending; _ Patches currently in -mm which might be from fweisbec@xxxxxxxxx are linux-next.patch posix_cpu_timer-consolidate-expiry-time-type.patch posix_cpu_timers-consolidate-timer-list-cleanups.patch posix_cpu_timers-consolidate-expired-timers-check.patch selftests-add-basic-posix-timers-selftests.patch posix-timers-correctly-get-dying-task-time-sample-in-posix_cpu_timer_schedule.patch posix_timers-fix-racy-timer-delta-caching-on-task-exit.patch mm-trace-filemap-add-and-del.patch mm-trace-filemap-add-and-del-v2.patch printk-tracing-rework-console-tracing.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html