SystemResource

Resources / SystemResource_Extend
Block Name: SystemResource_Extend

Code File Location: VisualSim/actor/lib/Scheduler_HW

Block Overview

o Used to define a processing resource that can be called from multiple points in a model.

o Separate the behavior flow from the architecture definition.

o Similar to the System resource methodology in SysML.

o Different from SystemResource. The output port of this block connects to behaviors, mappers and other delays. Adding the SystemResource_Done will return the Data Structure to the Mapper block.

o Supports Power_Manager switching. View Power Manager documentation for more details.
o Use the getBlockStatus (“Scheduler Name”, “Any value”, Type, Any value, Any value). Type can be “length, “copy” and “stats”. To learn the usage, click on getBlockStatus example.

Scheduler_HW

Description

The following is a block diagram that shows the application of a SystemResource_Extend block.

Scheduler_HW

This block forms the architecture part of the behavior and architecture separation methodology. In this methodology, the data structures are transfered along the behavior flow. When the data structure arrives at a Mapper block or a Mapper RegEx (scheduleTask) in a Script block, the Data Structure is sent to the architecture device defined by this SystemResource block. Another SystemResource can also send a request to this block. The SystemResource_Extend behaves as a Queue + Server + External Resource.

The arriving transaction is placed in a priority queue which is reordered based on the priority of the transaction. Higher the number; higher the priority. When the transaction arrives at the Head of the Queue, it is delayed by the "Task_Time" value provided along with the Data Structure. After this delay, the Data Structure is sent to the output port. Any logic can be performed outside of this block including delays, routing and trigger other operations. The SystemResource is blocked and no new transaction is processed. To use the SystemResource in non-blocking model, select the FCFS_NonBlocking for the Scheduler. When the SystemResource_Done block is encountered in the flow from the output port., the transaction releases the Scheduler and returns the transaction back to the SystemResource, Mapper or the next line after the RegEx function in the code. The transaction can continue through the SystemResource_Done block.

The external processing is used where the Server requires data from a cache before the completing the processing, or the data needs to be cleared by a interrupt before allowing the next transaction or to emulate a pipeline stall for a period of time. The SystemResource_Done Block can be executed immediately (non-blocking case), or at the end of the task (blocking case).

The ports are for plotting (state_plot) and external transaction processing (output). The incoming transaction to the SystemResource must provide the following information- Scheduler_Name, Task Time, Task_Priority (optional) and Task_Number (Identifier used for plotting purpose. If the default is unchanged, the Task_Number = 1).

The statistics can be accessed using the ResourceStatistics block, getBlockStatus and the output file that is written into the model directory/results folder.

To understand the usage of the SystemResource_Extend, look at the Scheduler Example in the BDE.

Key Features

o Input queue is ordered based on the priority of the transaction. Higher the number signifies higher priority.

o The Scheduler can handle time as a double value (number of seconds) or cycles (divided by the Speed_MHz).

o Three default scheduling schemes and two user-defined are provided. The FCFS_NonBlocking is to support non-blocking, which means that the next transaction does have to wait for the previous one to reach the Done block.

o Additional logic and delays can be added to each tasks by adding blocks to the 'output' port. The Scheduler is released using the Scheduler_Release.

o Requesting transaction can arrive from any part of the model.

o Supports two Power_Manager states- Active and Standby. Standby is when the SystemResource is inactive. Active is when the SystemResource is processing a task.

o User can define additional states for each SystemResource. Using the Power RegEx, the user can move the SystemResource into any state.
o getBlockStatus (“Scheduler Name”, “Any value”, Type, Any value, Any value). Type can be “length, “copy” and “stats”. Does not require Queue number or Position. To learn the usage, click on getBlockStatus example.

Scheduling Algorithms

o In the First-Come First_Serve (FCFS) mode, the Data Structure is processed when it reaches the head of the Queue.
o In the Round-Robin mode, the Data Structures in the Queue are each allocated a finite piece (Round-Robin Time Slice) of the processing time in each round. The RR scheduler will reduce a remaining task time by the time slice till completed. RR schedulers do not use priority.

In the Scheduler_FCFS_NonBlocking, when the first data structure is sent on the output, the next data structure can be delayed. There can be multiple data structure between the output port and the Done block.

o User-Defined: Users can add additional algorithms to the block. The Scheduler logic must be written in Java and samples are provided in <VisualSim_Install>/VS_AR/User_Library/algorithms directory.

Time Computation

The latency across the SystemResource_Extend consists of the queuing time + internal processing time + external processing time. The processing time is computed in two ways:

Time_Type = 'Relative_Time'. In this case the Task_Time in the Mapper blocks is the delay time at the Server. The Clock_Rate_Mhz of the SystemResource_Extend is ignored. In this mode, the Scheduler does not synchronize to clock boundaries. This is the primary difference with the 'Number_Clocks' option.

Time_Type = 'Number_Clocks'. In this case, the Task_Time in the Mapper blocks is the number of cycles. The Clock_Rate_Mhz of the SystemResource_Extend is used. The Delay Time = Task_Time / Clock_Rate_Mhz. If the Data Structure arrives out of sync with the clock, the processing will not start until the next clock cycle.

If a Mapper Block sends Task_Time '10.0' anticipating "Number Clocks" block menu attribute, and the block menu attribute is "Relative Time", then one may not see any output till '10.0' seconds!

The Context_Switching time occurs every time there is a new Data Structure processed or a Data Structure is preempted or a preemption Data Structure returns. The "Task_Context_Switch_Time" is not applied to each RR time slice, rather at the completion of a RR task.

Key Difference between SystemResource and SystemResource_Extend

Features	SystemResource	SystemResource_Extend
Preemption	Yes	No
Hierarchical	Yes	No
Extended Task Processing	No	Yes
Non-Blocking	No	Yes

Individual Statistics

The Scheduler blocks provide individual task timing and scheduler statistics. The user can enable this feature by checking the parameter called Add_Scheduler_Times_to_DS. This enables individual statistics to be added to each data structure processed by the Scheduler. The added fields include TIME_ACTIVATION, TIME_FINISH, TIME_IN_SCHEDULER, TIME_RELEASE and TIME_RESPONSE. These five fields complement the existing header field of a data structure called TIME, which contains the time the data structure was created, and appear together in the data structure.

Individual_Stats_Scheduler

TIME_ACTIVATION: The time the task, or thread, arrives at the scheduler for execution. If the scheduler is not busy, then the task will start to execute. If the scheduler is busy, then the task will be enqueued.
TIME_FINISH: The time taken by the task to complete the execution.
TIME_IN_SCHEDULER: This a convenience statistic calculated by subtracting the TIME_ACTIVATION from the TIME_FINISH, and represents the total time the task was in the scheduler: TIME_IN_SCHEDULER = TIME_FINISH - TIME_ACTIVATION.
TIME_RELEASE: This is the time at which the task starts executing on the scheduler. This time can vary depending on the scheduler loading. If the scheduler is not busy, or if the scheduler is busy, and the Scheduler_Type is FCFS + Preempt with the incoming task having a higher priority, then:

TIME_RELEASE = TIME_ACTIVATION

If the scheduler is busy, and enqueued, and the Scheduler_Type is FCFS then:

TIME_RELEASE > TIME_ACTIVATION.

TIME_RESPONSE: This is a convience statistic calculated by subtracting the TIME_RELEASE from the TIME_FINISH, and represents the time the scheduler spent processing the task. In terms of the added timestamps:

TIME_RESPONSE = TIME_FINISH - TIME_RELEASE

If the TIME_ACTIVATION and TIME_RELEASE timestamps are the same, then the TIME_IN_SCHEDULER and TIME_RESPONSE scheduler statistics are the same for the scheduler. To learn more about the individual statistics in a model, view the Individual Statistics Example in the BDE.

Multiple SystemResources

If multiple SystemResource exist in the model and Add_Scheduler_Times_to_DS is checked in multiple schedulers, then the user must process the added scheduler statistics after each scheduler completes execution by transferring the values to other data structure fields, or to unique model memories.

Statistics

The statistics for the Scheduler are generated using the getBlockStatus RegEx function. This function can be called in either the Virtual_Machine, Processing or Decision blocks.

    Statistics_A = getBlockStatus(Scheduler_Name,"Any Value","stats",1,"Any Value") -> To get the statistics

    Reset_Stats_A = getBlockStatus(Scheduler_Name,"Any Value","stats",-1,"Any Value")   -> To reset the statistics

    There is a pre-created statistics Generator block called Results/Resource_Statistics/Resource_Statistics_Report and is used in the Resource_Statistics Example in the BDE.

    View the SystemResource_Extend Example in the BDE to see the plotting.

Statistics Output

Statistic Name	Value	Explanation	Mathematical Equation	Type
Number_Entered	100	Number of transactions entering the queue.	-	int
Number_Exited	25	Number of transactions that left the queue.	-	int
Number_Rejected	10	Number of transactions rejected and output to reject port.	-	int
Queue_Number	1	Queue Number. Value will be 1.	-	int
Occupancy_Min	4.0	Minimum queue size during the simulation.	// Obtain Min for X, where X0 = Double.MAX_VALUE if (Xn < Xn – 1) Xmin = Xn	double
Occupancy_Mean	8.0	Mean/Average queue size during the simulation	// Obtain Mean for X Xµ = (1 / n) * (X1 + X2 + … + Xn)	double
Occupancy_StDev	3.0	Standard Deviation from the Mean queue size during the simulation.	// Obtain Standard Deviation for X Xσ = Math.sqrt ((1 / n) * ((X1 - Xµ)2 + (X2 - Xµ)2 + … + (Xn - Xµ)2)) STDEV_90_PCT = 1.6448530004790 STDEV_95_PCT = 1.9599610823207 STDEV_99_PCT = 2.5758345145732	double
Occupancy_Max	25.0	Maximum queue size consumed during the simulation.	// Obtain Max for X, where X0 = Double.MIN_VALUE if (Xn > Xn – 1) Xmax = Xn	double
Total_Delay_Min	1.3	In seconds. Least time through the queue+server among all transactions.	// Obtain Min for X, where X0 = Double.MAX_VALUE if (Xn < Xn – 1) Xmin = Xn	double
Total_Delay_Mean	1.3	In seconds. Mean/Average time through the queue+server among all transactions.	// Obtain Mean for X Xµ = (1 / n) * (X1 + X2 + … + Xn)	double
Total_Delay_StDev	1.3	In seconds. Standard Deviation from the Mean time through the queue+server among all transactions.	// Obtain Standard Deviation for X Xσ = Math.sqrt ((1 / n) * ((X1 - Xµ)2 + (X2 - Xµ)2 + … + (Xn - Xµ)2)) STDEV_90_PCT = 1.6448530004790 STDEV_95_PCT = 1.9599610823207 STDEV_99_PCT = 2.5758345145732	double
Total_Delay_Max	1.3	In seconds. Maximum time through the queue+server among all transactions.	// Obtain Max for X, where X0 = Double.MIN_VALUE if (Xn > Xn – 1) Xmax = Xn	double
Utilization_Pct_Mean	0.0	Mean/Average utilization of the server portion only. Queue utilization not considered. Unit is in percentage.	// Obtain Mean for X Xµ = (1 / n) * (X1 + X2 + … + Xn)	double

Where n is the number of samples and X is occupancy or delay.

Parameter	Explanation	Type	Example
Resource_Name	Resource_Name is used by Mapper blocks, RegEx and child SystemResource to call this SystemResource. Note: It cannot be called by a child SystemResource_Extend.	String	"Resource_Name"
Task_Context_Switch_Time	It is used to model the time to switch between one scheduler task and the next task. If the value is greater than 0.0, and there is a waiting task, it is added to the starting task. In RR mode, applied after task completes. If hiearchical schedulers, then lower level scheduler (SystemResource) determines context switch time.	Double	0.0
Round_Robin_Time_Slice	Quantum time to switch between tasks in Round Robin Scheduler, meaning the time the scheduler will devote to each task incrementally till it completes in the scheduler. If the "Task_Context_Switch_Time" is greater than zero, then it will also be added between round robin tasks. If there is only one task executing, then there will be no "Task_Context_Switch_Time" time added.	Double	0.1
Clock_Rate_Mhz	It is used to model delays, only if the Time_Type is 'Number_Clocks'. Scheduler delay is 'Number_Clocks' divided by Clock_Rate_Mhz times 1000000.0 (clock cycle time).	Double	500.0
Max_Scheduler_Length	It is in terms of individual tasks. If the scheduler length is exceeded, then an exception will be generated.	Integer	30
Time_Type	'Relative_Time' mode can be used for estimating prototype tasks, or partially defined software tasks. 'Number_Clocks' can be used to model more detailed behavior, such as a bus.	Double	Relative_Type
Scheduler_Type	'Scheduler_FCFS' is a first-come- first-serve scheduler that supports priority. However it does not preempt the executing task if a higher priority task arrives before a lower priority task completes. 'Scheduler_RR' schedules tasks to complete in a round-robin fashion, using the 'Round_Robin_Time_Slice' parameter, if there is more than one task in the scheduler. 'Scheduler_FCFS_NonBlocking' is used when the SystemResource must operate in a non-blocking mode. This means multiple Data Structures can be executing betwene the output and the Done block. Scheduler_User_1 or Scheduler_User_2 can be user defined scheduler tasks, defined in Java code.	-	Scheduler_FCFS
Add_Scheduler_Times_to_DS	Add_Scheduler_Times_to_DS turns on or off the request for individual statistics.	-	-

Port	Explanation
task_output	This port receives the data structure after the internal processing time has elapsed.
task_plot	Output port sending SystemResource task plot information. One typically connects this port to a TimedPlotter block. See Plot_Type below for menu attribute setting for plots. If the Mapper has a Task_Number = Task_Number_Fld_Int_Dbl_Expr or default, then the Task_number =1 for that Mapper.

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