Commit 17406b82 authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Ingo Molnar
Browse files

softlockup: remove timestamp checking from hung_task 



Impact: saves sizeof(long) bytes per task_struct

By guaranteeing that sysctl_hung_task_timeout_secs have elapsed between
tasklist scans we can avoid using timestamps.

Signed-off-by: default avatarMandeep Singh Baines <msb@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 94be52dc

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -1241,7 +1241,6 @@ struct task_struct { 
#endif

#ifdef CONFIG_DETECT_HUNG_TASK

/* hung task detection */

	unsigned long last_switch_timestamp;

	unsigned long last_switch_count;

#endif

/* CPU-specific state of this task */

kernel/fork.c

+3 −5
Original line number Diff line number Diff line
@@ -639,6 +639,9 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk) 


	tsk->min_flt = tsk->maj_flt = 0;

	tsk->nvcsw = tsk->nivcsw = 0;

#ifdef CONFIG_DETECT_HUNG_TASK

	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;

#endif



	tsk->mm = NULL;

	tsk->active_mm = NULL;
@@ -1041,11 +1044,6 @@ static struct task_struct *copy_process(unsigned long clone_flags, 


	p->default_timer_slack_ns = current->timer_slack_ns;



#ifdef CONFIG_DETECT_HUNG_TASK

	p->last_switch_count = 0;

	p->last_switch_timestamp = 0;

#endif



	task_io_accounting_init(&p->ioac);

	acct_clear_integrals(p);

kernel/hung_task.c

+9 −39
Original line number Diff line number Diff line
@@ -34,7 +34,6 @@ unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 
 * Zero means infinite timeout - no checking done:

 */

unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;

static unsigned long __read_mostly hung_task_poll_jiffies;



unsigned long __read_mostly sysctl_hung_task_warnings = 10;
@@ -69,33 +68,17 @@ static struct notifier_block panic_block = { 
	.notifier_call = hung_task_panic,

};



/*

 * Returns seconds, approximately.  We don't need nanosecond

 * resolution, and we don't need to waste time with a big divide when

 * 2^30ns == 1.074s.

 */

static unsigned long get_timestamp(void)

{

	int this_cpu = raw_smp_processor_id();



	return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */

}



static void check_hung_task(struct task_struct *t, unsigned long now,

			    unsigned long timeout)

static void check_hung_task(struct task_struct *t, unsigned long timeout)

{

	unsigned long switch_count = t->nvcsw + t->nivcsw;



	if (t->flags & PF_FROZEN)

		return;



	if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {

	if (switch_count != t->last_switch_count) {

		t->last_switch_count = switch_count;

		t->last_switch_timestamp = now;

		return;

	}

	if ((long)(now - t->last_switch_timestamp) < timeout)

		return;

	if (!sysctl_hung_task_warnings)

		return;

	sysctl_hung_task_warnings--;
@@ -111,7 +94,6 @@ static void check_hung_task(struct task_struct *t, unsigned long now, 
	sched_show_task(t);

	__debug_show_held_locks(t);



	t->last_switch_timestamp = now;

	touch_nmi_watchdog();



	if (sysctl_hung_task_panic)
@@ -145,7 +127,6 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) 
{

	int max_count = sysctl_hung_task_check_count;

	int batch_count = HUNG_TASK_BATCHING;

	unsigned long now = get_timestamp();

	struct task_struct *g, *t;



	/*
@@ -168,19 +149,16 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) 
		}

		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */

		if (t->state == TASK_UNINTERRUPTIBLE)

			check_hung_task(t, now, timeout);

			check_hung_task(t, timeout);

	} while_each_thread(g, t);

 unlock:

	rcu_read_unlock();

}



static void update_poll_jiffies(void)

static unsigned long timeout_jiffies(unsigned long timeout)

{

	/* timeout of 0 will disable the watchdog */

	if (sysctl_hung_task_timeout_secs == 0)

		hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;

	else

		hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;

	return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;

}



/*
@@ -197,8 +175,6 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 
	if (ret || !write)

		goto out;



	update_poll_jiffies();



	wake_up_process(watchdog_task);



 out:
@@ -211,19 +187,13 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write, 
static int watchdog(void *dummy)

{

	set_user_nice(current, 0);

	update_poll_jiffies();



	for ( ; ; ) {

		unsigned long timeout;



		while (schedule_timeout_interruptible(hung_task_poll_jiffies));

		unsigned long timeout = sysctl_hung_task_timeout_secs;



		/*

		 * Need to cache timeout here to avoid timeout being set

		 * to 0 via sysctl while inside check_hung_*_tasks().

		 */

		while (schedule_timeout_interruptible(timeout_jiffies(timeout)))

			timeout = sysctl_hung_task_timeout_secs;

		if (timeout)



		check_hung_uninterruptible_tasks(timeout);

	}