local_scheduler.c File Reference

local_scheduler is a kernel module in charge of implementing task scheduling following a LST (Least Slack Time) algorithm. More...

#include "local_scheduler.h"
#include "../../include/kernel_pkg.h"
#include "../include/plasma.h"
#include "../include/services.h"
#include "packet.h"
#include "utils.h"

Include dependency graph for local_scheduler.c:

Functions
unsigned int	get_time_slice ()
void	init_scheduling_ptr (Scheduling **sched_ptr, int tcb_index)
void	clear_scheduling (Scheduling *scheduling_tcb)
void	update_slack_time (Scheduling *input_task, unsigned int current_time)
void	real_time_task (Scheduling *real_time_task, unsigned int period, int deadline, unsigned int execution_time)
unsigned int	round_robin ()
void	dynamic_slice_time (Scheduling *scheduled, unsigned int time)
void	update_real_time (unsigned int current_time)
Scheduling *	LST (unsigned int current_time)

Variables
Scheduling	scheduling [MAX_LOCAL_TASKS]
	Scheduling array with its size equal to the max number of task that can execute into the processor.
unsigned int	time_slice
	Time slice used to configure the processor to generate an interruption.
unsigned int	schedule_overhead = 500
	Used to dynamically estimate the scheduler overhead.
unsigned int	instant_overhead
	Used to dynamically estimate the scheduler overhead.
unsigned int	cpu_utilization = 0
	RT CPU utilization, only filled with RT constraints.

Detailed Description

local_scheduler is a kernel module in charge of implementing task scheduling following a LST (Least Slack Time) algorithm.

HEMPS VERSION - 8.0 - support for RT applications

Distribution: June 2016

Created by: Marcelo Ruaro - contact: marce.nosp@m.lo.r.nosp@m.uaro@.nosp@m.acad.nosp@m..pucr.nosp@m.s.br

Research group: GAPH-PUCRS - contact: ferna.nosp@m.ndo..nosp@m.morae.nosp@m.s@pu.nosp@m.crs.b.nosp@m.r

The main function of this module is the LST algorithm, which is called by kernel_slave. It returns the pointer for the selected task to execute into the processor. This module is used only by the slave kernel

Function Documentation

void clear_scheduling

(

Scheduling *

scheduling_tcb

)

Clear a scheduling instance, used when the task is removed from slave processor

Parameters

scheduling_tcb

Scheduling pointer to be cleared

void dynamic_slice_time ( Scheduling *  scheduled, unsigned int  time  )

inline

This algorithm try to given an extra time slice to task selected by LST. The main approach is looking for the READY task slack time and the closer end of period

Parameters

scheduled	Scheduled task pointer
time	Current system time

unsigned int get_time_slice

(

)

Get the time slice. Useful to provide the kernel slave time slice

Returns

Global variable time_slice

void init_scheduling_ptr	(	Scheduling **	sched_ptr,
		int	tcb_index
	)

Initializes the scheduling array with valid pointers

Parameters

sched_ptr	Pointer to pointer of the scheduler variable into TCB structure
tcb_index	TCB array index

Scheduling* LST

(

unsigned int

current_time

)

The LST algorithm called by kernel slave. It select the next RT task with the least slack time, or the next BE task following a round-robin order

Parameters

current_time

Current system time

Returns

The Scheduling pointer of the scheduled task

void real_time_task	(	Scheduling *	real_time_task,
		unsigned int	period,
		int	deadline,
		unsigned int	execution_time
	)

Funcion called by kernel slave when a task call the primitive RealTime. This function set the real-time paramenters for the task.

Parameters

real_time_task	Task pointer that change or is setting its RT parameters
period	Task period in clock cycles
deadline	Task deadline in clock cycles
execution_time	Task execution time in clock cycles

unsigned int round_robin

(

)

A simple round-robin scheduler

Returns

The next round index

void update_real_time ( unsigned int  current_time )

inline

Updates the dynamic RT parameters for all RT tasks. The dynamic RT parameters are: remaining execution time, status, slack-time

Parameters

current_time

Current system time

void update_slack_time ( Scheduling *  input_task, unsigned int  current_time  )

inline

Updates the task slack time. The slack time is the time until the task start the next period, once it finishes it execution time for the current period

Parameters

input_task	Scheduling structure of the task to be updated
current_time	Current system time