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Diffstat (limited to '')
-rw-r--r-- | doc/user/cpuuse.t | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/doc/user/cpuuse.t b/doc/user/cpuuse.t index 161df741cd..4c67c58432 100644 --- a/doc/user/cpuuse.t +++ b/doc/user/cpuuse.t @@ -1,5 +1,5 @@ @c -@c COPYRIGHT (c) 1988-2002. +@c COPYRIGHT (c) 1988-2007. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @@ -22,11 +22,28 @@ The routines provided by the CPU usage statistics manager are: @section Background -@section Operations +When analyzing and debugging real-time applications, it is important +to be able to know how much CPU time each task in the system consumes. +This support component provides a mechanism to easily obtain this +information with little burden placed on the target. + +The raw data is gathered as part of performing a context switch. RTEMS +keeps track of how many clock ticks have occurred which the task being +switched out has been executing. If the task has been running less than +1 clock tick, then for the purposes of the statistics, it is assumed to +have executed 1 clock tick. This results in some inaccuracy but the +alternative is for the task to have appeared to execute 0 clock ticks. + +RTEMS versions newer than the 4.7 release series, support the ability +to obtain timestamps with nanosecond granularity if the BSP provides +support. It is a desirable enhancement to change the way the usage +data is gathered to take advantage of this recently added capability. +Please consider sponsoring the core RTEMS development team to add +this capability. -@section Report CPU Usage Statistics +@section Operations -@subsection Reporting Period Statistics +@subsection Report CPU Usage Statistics The application may dynamically report the CPU usage for every task in the system by calling the @@ -72,7 +89,7 @@ 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 +@subsection Reset CPU Usage Statistics Invoking the @code{@value{DIRPREFIX}cpu_usage_reset} routine resets the CPU usage statistics for all tasks in the system. @@ -110,7 +127,7 @@ all tasks in the system. @subheading NOTES: -NONE +The table is printed using the @code{printk} routine. @page @subsection cpu_usage_reset - Reset CPU Usage Statistics |