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Commit dcade5ed authored by Dimitri Sivanich's avatar Dimitri Sivanich Committed by Linus Torvalds
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SGI Altix IA64 mmtimer: eliminate long interval timer holdoffs 



This patch for SGI Altix/IA64 eliminates interval long timer holdoffs in
cases where we don't start an interval timer before the expiration time.
This sometimes happens when a number of interval timers on the same shub
with the same interval run simultaneously.

Signed-off-by: default avatarDimitri Sivanich <sivanich@sgi.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 656e17ea

drivers/char/mmtimer.c

+32 −28
Original line number Diff line number Diff line
@@ -176,9 +176,9 @@ static void mmtimer_setup_int_2(int cpu, u64 expires) 
 * in order to insure that the setup succeeds in a deterministic time frame.

 * It will check if the interrupt setup succeeded.

 */

static int mmtimer_setup(int cpu, int comparator, unsigned long expires)

static int mmtimer_setup(int cpu, int comparator, unsigned long expires,

	u64 *set_completion_time)

{



	switch (comparator) {

	case 0:

		mmtimer_setup_int_0(cpu, expires);
@@ -191,7 +191,8 @@ static int mmtimer_setup(int cpu, int comparator, unsigned long expires) 
		break;

	}

	/* We might've missed our expiration time */

	if (rtc_time() <= expires)

	*set_completion_time = rtc_time();

	if (*set_completion_time <= expires)

		return 1;



	/*
@@ -227,6 +228,8 @@ static int mmtimer_disable_int(long nasid, int comparator) 
#define TIMER_OFF	0xbadcabLL	/* Timer is not setup */

#define TIMER_SET	0		/* Comparator is set for this timer */



#define MMTIMER_INTERVAL_RETRY_INCREMENT_DEFAULT 40



/* There is one of these for each timer */

struct mmtimer {

	struct rb_node list;
@@ -242,6 +245,11 @@ struct mmtimer_node { 
};

static struct mmtimer_node *timers;



static unsigned mmtimer_interval_retry_increment =

	MMTIMER_INTERVAL_RETRY_INCREMENT_DEFAULT;

module_param(mmtimer_interval_retry_increment, uint, 0644);

MODULE_PARM_DESC(mmtimer_interval_retry_increment,

	"RTC ticks to add to expiration on interval retry (default 40)");



/*

 * Add a new mmtimer struct to the node's mmtimer list.
@@ -289,7 +297,8 @@ static void mmtimer_set_next_timer(int nodeid) 
	struct mmtimer_node *n = &timers[nodeid];

	struct mmtimer *x;

	struct k_itimer *t;

	int o;

	u64 expires, exp, set_completion_time;

	int i;



restart:

	if (n->next == NULL)
@@ -300,7 +309,8 @@ static void mmtimer_set_next_timer(int nodeid) 
	if (!t->it.mmtimer.incr) {

		/* Not an interval timer */

		if (!mmtimer_setup(x->cpu, COMPARATOR,

					t->it.mmtimer.expires)) {

					t->it.mmtimer.expires,

					&set_completion_time)) {

			/* Late setup, fire now */

			tasklet_schedule(&n->tasklet);

		}
@@ -308,14 +318,23 @@ static void mmtimer_set_next_timer(int nodeid) 
	}



	/* Interval timer */

	o = 0;

	while (!mmtimer_setup(x->cpu, COMPARATOR, t->it.mmtimer.expires)) {

		unsigned long e, e1;

		struct rb_node *next;

		t->it.mmtimer.expires += t->it.mmtimer.incr << o;

		t->it_overrun += 1 << o;

		o++;

		if (o > 20) {

	i = 0;

	expires = exp = t->it.mmtimer.expires;

	while (!mmtimer_setup(x->cpu, COMPARATOR, expires,

				&set_completion_time)) {

		int to;



		i++;

		expires = set_completion_time +

				mmtimer_interval_retry_increment + (1 << i);

		/* Calculate overruns as we go. */

		to = ((u64)(expires - exp) / t->it.mmtimer.incr);

		if (to) {

			t->it_overrun += to;

			t->it.mmtimer.expires += t->it.mmtimer.incr * to;

			exp = t->it.mmtimer.expires;

		}

		if (i > 20) {

			printk(KERN_ALERT "mmtimer: cannot reschedule timer\n");

			t->it.mmtimer.clock = TIMER_OFF;

			n->next = rb_next(&x->list);
@@ -323,21 +342,6 @@ static void mmtimer_set_next_timer(int nodeid) 
			kfree(x);

			goto restart;

		}



		e = t->it.mmtimer.expires;

		next = rb_next(&x->list);



		if (next == NULL)

			continue;



		e1 = rb_entry(next, struct mmtimer, list)->

			timer->it.mmtimer.expires;

		if (e > e1) {

			n->next = next;

			rb_erase(&x->list, &n->timer_head);

			mmtimer_add_list(x);

			goto restart;

		}

	}

}