@c @c COPYRIGHT (c) 1988-2002. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @c @chapter CPU Usage Statistics @section Introduction The CPU usage statistics manager is an RTEMS support component that provides a convenient way to manipulate the CPU usage information associated with each task The routines provided by the CPU usage statistics manager are: @itemize @bullet @item @code{CPU_usage_Dump} - Report CPU Usage Statistics @item @code{CPU_usage_Reset} - Reset CPU Usage Statistics @end itemize @section Background @section Operations @section Report CPU Usage Statistics @subsection Reporting Period Statistics The application may dynamically report the CPU usage for every task in the system by calling the @code{CPU_usage_Dump} routine. This routine prints a table with the following information per task: @itemize @bullet @item task id @item task name @item number of clock ticks executed @item percentage of time consumed by this task @end itemize The following is an example of the report generated: @example @group CPU Usage by thread ID NAME TICKS PERCENT 0x04010001 IDLE 0 0.000 0x08010002 TA1 1203 0.748 0x08010003 TA2 203 0.126 0x08010004 TA3 202 0.126 Ticks since last reset = 1600 Total Units = 1608 @end group @end example Notice that the "Total Units" is greater than the ticks per reset. This is an artifact of the way in which RTEMS keeps track of CPU usage. When a task is context switched into the CPU, the number of clock ticks it has executed is incremented. While the task is executing, this number is incremented on each clock tick. Otherwise, if a task begins and completes execution between successive clock ticks, there would be no way to tell that it executed at all. Another thing to keep in mind when looking at idle time, is that many systems -- especially during debug -- have a task providing some type of debug interface. It is usually fine to think of the total idle time as being the sum of the IDLE task and a debug task that will not be included in a production build of an application. @section Reset CPU Usage Statistics Invoking the @code{CPU_usage_Reset} routine resets the CPU usage statistics for all tasks in the system. @section Directives This section details the CPU usage statistics manager's directives. A subsection is dedicated to each of this manager's directives and describes the calling sequence, related constants, usage, and status codes. @page @subsection CPU_usage_Dump - Report CPU Usage Statistics @subheading CALLING SEQUENCE: @ifset is-C @example void CPU_usage_Dump( void ); @end example @end ifset @ifset is-Ada @example An Ada interface is not currently available. @end example @end ifset @subheading STATUS CODES: NONE @subheading DESCRIPTION: This routine prints out a table detailing the CPU usage statistics for all tasks in the system. @subheading NOTES: NONE @page @subsection CPU_usage_Reset - Reset CPU Usage Statistics @subheading CALLING SEQUENCE: @ifset is-C @example void CPU_usage_Reset( void ); @end example @end ifset @ifset is-Ada @example An Ada interface is not currently available. @end example @end ifset @subheading STATUS CODES: NONE @subheading DESCRIPTION: This routine re-initializes the CPU usage statistics for all tasks in the system to their initial state. The initial state is that a task has not executed and thus has consumed no CPU time. default state which is when zero period executions have occurred. @subheading NOTES: NONE