Posix timers: limit number of timers firing at once

e80eda94 · Linus Torvalds <[email protected]> · 2005-10-23 10:02:50 -07:00

Bursty timers aren't good for anybody, very much including latency for
other programs when we trigger lots of timers in interrupt context.  So
set a random limit, after which we'll handle the rest on the next timer
tick.

Noted by Oleg Nesterov <[email protected]>

Signed-off-by: Linus Torvalds <[email protected]>

Commit: e80eda94d3eaf1d12cfc97878eff77cd679dabc9
Parents: d475f3f4

Changes

1 files changed · +14 −6

File	Status	Add	Del	Content
kernel/posix-cpu-timers.c	modified	+14	−6	View file

kernel/posix-cpu-timers.c

View file

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 7a51a55..d30b304 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -961,14 +961,16 @@ void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp)
 static void check_thread_timers(struct task_struct *tsk,
 				struct list_head *firing)
 {
+	int maxfire;
 	struct list_head *timers = tsk->cpu_timers;
 
+	maxfire = 20;
 	tsk->it_prof_expires = cputime_zero;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (cputime_lt(prof_ticks(tsk), t->expires.cpu)) {
+		if (!--maxfire || cputime_lt(prof_ticks(tsk), t->expires.cpu)) {
 			tsk->it_prof_expires = t->expires.cpu;
 			break;
 		}
@@ -977,12 +979,13 @@ static void check_thread_timers(struct task_struct *tsk,
 	}
 
 	++timers;
+	maxfire = 20;
 	tsk->it_virt_expires = cputime_zero;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (cputime_lt(virt_ticks(tsk), t->expires.cpu)) {
+		if (!--maxfire || cputime_lt(virt_ticks(tsk), t->expires.cpu)) {
 			tsk->it_virt_expires = t->expires.cpu;
 			break;
 		}
@@ -991,12 +994,13 @@ static void check_thread_timers(struct task_struct *tsk,
 	}
 
 	++timers;
+	maxfire = 20;
 	tsk->it_sched_expires = 0;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (tsk->sched_time < t->expires.sched) {
+		if (!--maxfire || tsk->sched_time < t->expires.sched) {
 			tsk->it_sched_expires = t->expires.sched;
 			break;
 		}
@@ -1013,6 +1017,7 @@ static void check_thread_timers(struct task_struct *tsk,
 static void check_process_timers(struct task_struct *tsk,
 				 struct list_head *firing)
 {
+	int maxfire;
 	struct signal_struct *const sig = tsk->signal;
 	cputime_t utime, stime, ptime, virt_expires, prof_expires;
 	unsigned long long sched_time, sched_expires;
@@ -1045,12 +1050,13 @@ static void check_process_timers(struct task_struct *tsk,
 	} while (t != tsk);
 	ptime = cputime_add(utime, stime);
 
+	maxfire = 20;
 	prof_expires = cputime_zero;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (cputime_lt(ptime, t->expires.cpu)) {
+		if (!--maxfire || cputime_lt(ptime, t->expires.cpu)) {
 			prof_expires = t->expires.cpu;
 			break;
 		}
@@ -1059,12 +1065,13 @@ static void check_process_timers(struct task_struct *tsk,
 	}
 
 	++timers;
+	maxfire = 20;
 	virt_expires = cputime_zero;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (cputime_lt(utime, t->expires.cpu)) {
+		if (!--maxfire || cputime_lt(utime, t->expires.cpu)) {
 			virt_expires = t->expires.cpu;
 			break;
 		}
@@ -1073,12 +1080,13 @@ static void check_process_timers(struct task_struct *tsk,
 	}
 
 	++timers;
+	maxfire = 20;
 	sched_expires = 0;
 	while (!list_empty(timers)) {
 		struct cpu_timer_list *t = list_entry(timers->next,
 						      struct cpu_timer_list,
 						      entry);
-		if (sched_time < t->expires.sched) {
+		if (!--maxfire || sched_time < t->expires.sched) {
 			sched_expires = t->expires.sched;
 			break;
 		}