RE: [EXTERNAL] Re: [XEN PATCH v3] xen/arinc653: fix delay in the start of major frame

["Choi, Anderson" <Anderson.Choi@xxxxxxxxxx>]

Stewart,

> EXT email: be mindful of links/attachments.
> 
> Hi,
> 
> It largely looks OK to me, just a few small comments below.
> 
> On 7/18/25 05:16, Anderson Choi wrote:
>> ARINC653 specificaion requires partition scheduling to be
>> deterministic
> 
> Typo: s/specificaion/specification/
>
Addressed the typo.

ARINC653 specification requires partition scheduling to be deterministic

>> Per discussion with Nathan Studer, there are odd cases the first minor
>> frame can be also missed. In that sceanario, iterate through the
>> schedule after resyncing
> 
> Typo: s/sceanario/scenario/
> 
> The line is also too long.
> 
Addressed the typo and the lengthy sentence.

Per discussion with Nathan Studer, there are odd cases the first minor
frame can be also missed. In that scenario, iterate through the schedule
after resyncing the expected next major frame.

>> Per suggestion from Stewart Hildebrand, the while loop to calculate
>> the start of next major frame can be eliminated by using a modulo
> operation.
> 
> The while loop was only in earlier revisions of the patch, not in the upstream
> codebase, so it doesn't make sense to mention it in the commit message.
>
Removed the reference to the while loop.

Per suggestion from Stewart Hildebrand, use a modulo operation to
calculate the start of next major frame.

>> 
>> Fixes: 22787f2e107c ("ARINC 653 scheduler")
>> 
> 
> Please remove the extraneous newline between the Fixes: tag and
> remaining tags
> 
Removed the newline.

Fixes: 22787f2e107c ("ARINC 653 scheduler")
Suggested-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
Suggested-by: Nathan Studer <nathan.studer@xxxxxxxxxxxxxxx>
Signed-off-by: Anderson Choi <anderson.choi@xxxxxxxxxx>

>> @@ -526,29 +528,30 @@ a653sched_do_schedule(
>> 
>>      spin_lock_irqsave(&sched_priv->lock, flags);
> 
> Since the num_schedule_entries < 1 case is no longer handled below, we
> depend on major_frame > 0. Please add ASSERT(sched_priv->major_frame >
> 0); here.
>
>> -    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 directly eliminating the use of
>> + loop */
> 
> Similarly to the commit message, there was no loop in the code before, it
> doesn't make sense to mention it in the in-code comment.
>
Added ASSERT() and removed the mention to the loop.

     spin_lock_irqsave(&sched_priv->lock, flags);

-    /* Switch to next major frame directly eliminating the use of loop */
+    ASSERT(sched_priv->major_frame > 0);
+
+    /* Switch to next major frame using a modulo operation */

>> +    if ( 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 */
>> +        s_time_t major_frame = sched_priv->major_frame;
>> +        s_time_t remainder = (now - sched_priv->next_major_frame) %
>> + major_frame;
>> +
>> +        /* major_frame and schedule[0].runtime contain DEFAULT_TIMESLICE
>> +         * if num_schedule_entries is zero.
>> +         */
> 
> The start of the multi-line comment should be on its own line. I know the
> comment format was a preexisting issue, but since you are changing the lines
> anyway, please adhere to CODING_STYLE on the changed lines.
> 
Addressed as below.

-        /* major_frame and schedule[0].runtime contain DEFAULT_TIMESLICE
+        /*
+         * major_frame and schedule[0].runtime contain DEFAULT_TIMESLICE
          * if num_schedule_entries is zero.
          */
         sched_priv->sched_index = 0;

>> +        sched_priv->sched_index++;
>> +        sched_priv->next_switch_time +=
>> +            sched_priv->schedule[sched_priv->sched_index].runtime;
>>      }
>> -
>> +
> 
> Please remove the extraneous white space
> 
Removed the white space.

I do appreciate your valuable review.
Would it be okay to submit v4 with all the changes applied?
Please let me know if there's anything that doesn't reflect your comments 
correctly.

Thanks,
Anderson