Scheduling - Revision history

Suhridk: /* Sporadic Parameters */

2012-01-10T22:34:34Z

Sporadic Parameters

Suhridk: /* Release Parameters */

2012-01-10T18:06:35Z

Release Parameters

Suhridk: /* Policy */

2012-01-10T17:48:16Z

Policy

Suhridk: /* Changes to Parameter Classes = */

2012-01-10T17:36:10Z

Changes to Parameter Classes =

Suhridk: /* Sporadic Parameters */

2012-01-10T17:35:49Z

Sporadic Parameters

Suhridk: /* Aperiodic Parameters */

2012-01-01T23:47:40Z

Aperiodic Parameters

Suhridk: /* Sporadic Parameters */

2012-01-01T23:43:59Z

Sporadic Parameters

Suhridk: /* Sporadic Parameters */

2012-01-01T23:41:22Z

Sporadic Parameters

Suhridk: /* Aperiodic Parameters */

2012-01-01T23:40:25Z

Aperiodic Parameters

Suhridk at 20:03, 1 January 2012

2012-01-01T20:03:17Z

@@ Line 128: / Line 128: @@
 ** Except: Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the fire() method shall throw MITViolationException.
 ** Ignore - Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the new arrival time is ignored.
-** Save - Under this policy the arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters is not compared to the specified minimum interarrival time. Saves the event in the Q. '''However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.'''
+** Save - Under this policy the arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters is not compared to the specified minimum interarrival time. Saves the event in the Q. '''However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.'''  For the save policy, the key point is that the fireCount will not be incremented until the
 ** Replace - Under this policy if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the information for this arrival''' replaces a previous arrival.'''

← Older revision		Revision as of 18:06, 10 January 2012
Line 94:		Line 94:

	* Minimum info that a scheduler needs to perform feasibility analysis is cost and deadline.		* Minimum info that a scheduler needs to perform feasibility analysis is cost and deadline.
		+
		+	=== Cost Enforcement ===
		+
		+	* the RTSJ requires that the priority scheduler gives a schedulable object a CPU budget of no more than its cost value on each release.
		+	* if a schedulable objects overrun its cost budget, it is automatically descheduled (made not eligible for execution) '''immediately'''
		+	* it will not be re-scheduled until either its next release occurs (in which case its budget is replenished) or its associated cost value is increased.

	=== Periodic Parameters ===		=== Periodic Parameters ===

@@ Line 163: / Line 163: @@
 === Policy ===
-* Orders SO's according to policy.
+* Orders SO's according to priority.
 * Supports 28 different RT Priorities.
 * Programmer can define priorities. Priorities can be changed at run-time.

@@ Line 179: / Line 179: @@
 * Requires no particular analysis to be supported.
-=== Changes to Parameter Classes ====
+=== Changes to Parameter Classes ===
 * Under the priority scheduler, changes to scheduling, release, memory, and processing group parameters take effect as follows:

@@ Line 122: / Line 122: @@
 ** Except: Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the fire() method shall throw MITViolationException.
 ** Ignore - Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the new arrival time is ignored.
-** Save - Under this policy the arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters is not compared to the specified minimum interarrival time. Saves the event in the Q. However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.
+** Save - Under this policy the arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters is not compared to the specified minimum interarrival time. Saves the event in the Q. '''However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.'''
 ** Replace - Under this policy if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the information for this arrival''' replaces a previous arrival.'''

@@ Line 106: / Line 106: @@
 * Programmer can specify length of queue and action to be taken when Q overflows. e.g. setArrivalTimeQueueOverflowBehavior(String policy) where policy can be EXCEPT, IGNORE, REPLACE, SAVE which specifies what
 to do in the Q when a release event occurs and the Q is full.
-** EXCEPT: Under this policy, if an arrival occurs and its time should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the fire() method shall throw a ArrivalTimeQueueOverflowException.
+** EXCEPT: Under this policy, if an arrival occurs and its time should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the fire() method (the fire() method thrown by the AsyncEvent) shall throw a ArrivalTimeQueueOverflowException.
 ** IGNORE: Under this policy, if an arrival occurs and its time should be queued, but the queue already holds a number of times equal to the initial queue length defined by this then the arrival is ignored.
 ** REPLACE:Under this policy if an arrival occurs and should be queued but the queue already holds a number of times equal to the initial queue length defined by this then the information for this arrival '''replaces a previous arrival.'''

@@ Line 120: / Line 120: @@
 * Apart from the Q overflow behaviour, has a setMitViolationBehaviour(String policy) on what to do with release events that violate MIT - mitViolationIgnore, Except, Save, Replace.
-** Except throws an exception
+** Except: Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the fire() method shall throw MITViolationException.
-** Ignore - ignores the new violating release event.
+** Ignore - Under this policy, if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the new arrival time is ignored.
-** Save - saves the event in the Q. However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.
+** Save - Under this policy the arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters is not compared to the specified minimum interarrival time. Saves the event in the Q. However the time between this request and the other requests in the Q is set to the Minimum Inter Arrival time.
-** Replace - replaces the '''previous arrival''' in the Q.
+** Replace - Under this policy if an arrival time for any instance of Schedulable which has this as its instance of ReleaseParameters occurs at a time less then the minimum interarrival time defined here then the information for this arrival''' replaces a previous arrival.'''
 == Scheduling Parameters ==

@@ Line 113: / Line 113: @@
 === Sporadic Parameters ===
 * Released at irregular intervals, but any two releases will always occur at an interval greater than or equal to a minimum inter arrival time. (MIT)
 * The scheduler must check for violations of this constraint and take corrective action.
 * Again like Aperiodic, a sporadic SO might be released and before it completes, can be released again.
 * So it is necessary to queue the release events so that they arent lost.
-* Has a setMitViolationBehaviour(String policy) on what to do with release events that vilate mit - mitViolationIgnore, Except, Save, Replace.
+* Apart from the Q overflow behaviour, has a setMitViolationBehaviour(String policy) on what to do with release events that violate MIT - mitViolationIgnore, Except, Save, Replace.
 ** Except throws an exception

@@ Line 199: / Line 199: @@
 * At the end of the release, SO calls deschedule() which makes the EDF change its priority to high (ready for next release).
 * With this approach, a thread with a longer deadline will execute in preference to a shorter deadline thread but only for a small limited time when it is released
-* This can be ensured by encapsulating the calls to reschedule and deschedule. ??
+* This can be ensured by encapsulating the calls to reschedule and deschedule. [TODO : What?]