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: Dimitri Sivanich <sivanich@sgi.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 32 insertions, 28 deletions

diff --git a/drivers/char/mmtimer.c b/drivers/char/mmtimer.c
index c070b53984e4..e6d75627c6c8 100644
--- a/drivers/char/mmtimer.c
+++ b/drivers/char/mmtimer.c
@@ -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 @@ restart:
         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 @@ restart:
         }
 
         /* 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 @@ restart:
                         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;
-                }
         }
 }