On 7/17/25 9:21, Hildebrand, Stewart wrote:
> > - if ( sched_priv->num_schedule_entries < 1 )
> > - sched_priv->next_major_frame = now + DEFAULT_TIMESLICE;
> > - else if ( now >= sched_priv->next_major_frame )
> > + /* Switch to next major frame while handling potentially missed frames
> > */
> > + while ( now >= sched_priv->next_major_frame )
> > {
> > - /* time to enter a new major frame
> > - * the first time this function is called, this will be true */
> > - /* start with the first domain in the schedule */
> > sched_priv->sched_index = 0;
> > - sched_priv->next_major_frame = now + sched_priv->major_frame;
> > - sched_priv->next_switch_time = now +
> > sched_priv->schedule[0].runtime;
> > - }
> > - else
> > - {
> > - while ( (now >= sched_priv->next_switch_time) &&
> > - (sched_priv->sched_index <
> > sched_priv->num_schedule_entries) )
> > +
> > + if ( sched_priv->num_schedule_entries < 1 )
> > {
> > - /* time to switch to the next domain in this major frame */
> > - sched_priv->sched_index++;
> > - sched_priv->next_switch_time +=
> > - sched_priv->schedule[sched_priv->sched_index].runtime;
> > + sched_priv->next_major_frame += DEFAULT_TIMESLICE;
> > + sched_priv->next_switch_time =
> > + sched_priv->next_major_frame;
> > }
> > + else
> > + {
> > + sched_priv->next_switch_time = sched_priv->next_major_frame +
> > + sched_priv->schedule[0].runtime;
> > + sched_priv->next_major_frame += sched_priv->major_frame;
> > + }
> > + }
>
> There's no need for the above loop, this can be fixed by subtracting the
> remainder
> (modulus major_frame). E.g.:
>
> if ( now >= sched_priv->next_major_frame )
> {
> s_time_t major_frame = sched_priv->num_schedule_entries < 1
> ? DEFAULT_TIMESLICE
> : sched_priv->major_frame;
> s_time_t remainder = (now - sched_priv->next_major_frame) %
> major_frame;
>
> sched_priv->sched_index = 0;
> sched_priv->next_major_frame = now - remainder + major_frame;
> sched_priv->next_switch_time = now - remainder +
> (sched_priv->num_schedule_entries < 1
> ? DEFAULT_TIMESLICE
> : sched_priv->schedule[0].runtime);
> }
>
The direct method suggested by Stew is preferable in the unusual case where
many major frames are missed. (We have only seen that happen when using a
debugger.)
To help uncover any issues like the one this patch addresses in the future we
may also want to follow up this commit with a change to make scheduler misses
more obvious. Something like the following:
commit e95cbc9078127c412bd1605d93cb97837751b5b4 (HEAD -> master)
Author: Nathan Studer <nathan.stu...@dornerworks.com>
Date: Thu Jul 17 12:43:39 2025 -0400
Do not silently skip frame overruns
diff --git a/xen/common/sched/arinc653.c b/xen/common/sched/arinc653.c
index 2d0d3bcbb3..a2c1c66c27 100644
--- a/xen/common/sched/arinc653.c
+++ b/xen/common/sched/arinc653.c
@@ -523,9 +523,17 @@ a653sched_do_schedule(
a653sched_priv_t *sched_priv = SCHED_PRIV(ops);
const unsigned int cpu = sched_get_resource_cpu(smp_processor_id());
unsigned long flags;
+ unsigned int oindex;
+ unsigned int missed;
spin_lock_irqsave(&sched_priv->lock, flags);
+ if ( now > (sched_priv->next_major_frame + sched_priv->major_frame))
+ {
+ missed = (now - sched_priv->next_major_frame) /
sched_priv->major_frame;
+ printk(XENLOG_ERR, "Missed %d major frame(s)!\n", missed);
+ }
+
/* Switch to next major frame while handling potentially missed frames */
@@ -544,6 +552,7 @@ a653sched_do_schedule(
}
}
+ oindex = sched_priv->sched_index;
/* Switch minor frame or find correct minor frame after a miss */
while ( (now >= sched_priv->next_switch_time) &&
(sched_priv->sched_index < sched_priv->num_schedule_entries) )
@@ -553,6 +562,12 @@ a653sched_do_schedule(
sched_priv->schedule[sched_priv->sched_index].runtime;
}
+ if ( (oindex - sched_priv->sched_index) > 1)
+ {
+ missed = (oindex - sched_priv->sched_index - 1);
+ printk(XENLOG_WARNING, "Missed %d minor frame(s)!\n", missed);
+ }
+
/*
> The commit description may want some minor updating to reflect this.
>
> > +
> > + /* Switch minor frame or find correct minor frame after a miss */
> > + while ( (now >= sched_priv->next_switch_time) &&
> > + (sched_priv->sched_index < sched_priv->num_schedule_entries) )
> > + {
> > + sched_priv->sched_index++;
> > + sched_priv->next_switch_time +=
> > + sched_priv->schedule[sched_priv->sched_index].runtime;
> > }
> >
> > /*
