On Thu, Oct 07, 2010 at 03:42:56PM -0700, Andrew Morton wrote:
> On Thu, 7 Oct 2010 09:39:41 -0500
> Dimitri Sivanich <sivanich@xxxxxxx> wrote:
>
> > 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.
> >
>
> Grumble.
Ditto.
>
> > --- linux-2.6.orig/drivers/char/mmtimer.c 2010-10-07 09:34:29.837725250 -0500
> > +++ linux-2.6/drivers/char/mmtimer.c 2010-10-07 09:34:31.609948769 -0500
> > @@ -174,9 +174,8 @@ static void mmtimer_setup_int_2(int cpu,
> > * 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 *r)
>
> Choosing a variable's identifier is your last chance to explain to the
> reader what that variable does. And you blew it!
See the variable identifier in the attached patch. Better?
>
> >
> > ...
> >
> > +static unsigned mmtimer_intrvl_retry_incr = MMTIMER_INTRVL_RETRY_INCR_DEFAULT;
> > +module_param(mmtimer_intrvl_retry_incr, uint, 0644);
> > +MODULE_PARM_DESC(mmtimer_intrvl_retry_incr,
> > + "RTC ticks to add to expiration on interval retry (default 40)");
>
> And the problem with abbreviations like "intrvl" is that they're hard
> to remember. Which is why in the kernel we much prefer to use the
> entire English word.
>
Again, see the variable names in the attached patch.
>
> I'm unable to work out how important this patch is. I'm presently
> assuming 2.6.37.
Good enough.
__________________
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@xxxxxxx>
---
drivers/char/mmtimer.c | 60 ++++++++++++++++++++++++---------------------
1 file changed, 32 insertions(+), 28 deletions(-)
Index: linux-2.6/drivers/char/mmtimer.c
===================================================================
--- linux-2.6.orig/drivers/char/mmtimer.c 2010-10-08 08:14:45.971073581 -0500
+++ linux-2.6/drivers/char/mmtimer.c 2010-10-08 08:14:49.027447493 -0500
@@ -174,9 +174,9 @@ static void mmtimer_setup_int_2(int cpu,
* 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);
@@ -189,7 +189,8 @@ static int mmtimer_setup(int cpu, int co
break;
}
/* We might've missed our expiration time */
- if (rtc_time() <= expires)
+ *set_completion_time = rtc_time();
+ if (*set_completion_time <= expires)
return 1;
/*
@@ -225,6 +226,8 @@ static int mmtimer_disable_int(long nasi
#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;
@@ -240,6 +243,11 @@ 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.
@@ -287,7 +295,8 @@ static void mmtimer_set_next_timer(int n
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)
@@ -298,7 +307,8 @@ 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);
}
@@ -306,14 +316,23 @@ 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);
@@ -321,21 +340,6 @@ 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;
- }
}
}
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