URL
https://opencores.org/ocsvn/openrisc_me/openrisc_me/trunk
Subversion Repositories openrisc_me
[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [cpuload-functions.html] - Rev 28
Go to most recent revision | Compare with Previous | Blame | View Log
<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >CPU Load Measurements</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="CPU load measurements" HREF="services-cpuload.html"><LINK REL="PREVIOUS" TITLE="CPU load measurements" HREF="services-cpuload.html"><LINK REL="NEXT" TITLE="Application profiling" HREF="services-profile-gprof.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="services-cpuload.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="services-profile-gprof.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="CPULOAD-FUNCTIONS">Chapter 51. CPU Load Measurements</H1 ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SERVICES-CPULOAD-API">CPU Load API</H1 ><P >The package allows the CPU load to be estimated. The measurement code must first be calibrated to the target it is running on. Once this has been performed the measurement process can be started. This is a continuous process, so always providing the most up to data measurements. The process can be stopped at any time if required. Once the process is active, the results can be retrieved.</P ><P >Note that if the target/processor performs any power saving actions, such as reducing the clock speed, or halting until the next interrupt etc, these will interfere with the CPU load measurement. Under these conditions the measurement results are undefined. The synthetic target is one such system. See the implementation details at the foot of this page for further information. </P ><P >SMP systems are not supported, only uniprocessor system.</P ><P > The API for load measuring functions can be found in the file <TT CLASS="FILENAME" >cyg/cpuload/cpuload.h</TT >.</P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-CALIBRATE">cyg_cpuload_calibrate</H2 ><P >This function is used to calibrate the cpu load measurement code. It makes a measurement to determine the CPU properties while idle.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void cyg_cpuload_calibrate(cyg_uint32 *calibration);</PRE ></TD ></TR ></TABLE ><P >The function returns the calibration value at the location pointed to by <TT CLASS="PARAMETER" ><I >calibration</I ></TT >.</P ><P >This function is quite unusual. For it to work correctly a few conditions must be met. The function makes use of the two highest thread priorities. No other threads must be using these priorities while the function is being used. The kernel scheduler must be started and not disabled. The function takes 100ms to complete during which time no other threads will be run.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-CREATE">cyg_cpuload_create</H2 ><P >This function starts the CPU load measurments.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void cyg_cpuload_create(cyg_cpuload_t *cpuload, cyg_uint32 calibrate, cyg_handle_t *handle);</PRE ></TD ></TR ></TABLE ><P >The measurement process is started and a handle to it is returned in <TT CLASS="PARAMETER" ><I >*handle</I ></TT >. This handle is used to access the results and the stop the measurement process. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-DELETE">cyg_cpuload_delete</H2 ><P >This function stops the measurement process. </P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void cyg_cpuload_delete(cyg_handle_t handle);</PRE ></TD ></TR ></TABLE ><P ><TT CLASS="PARAMETER" ><I >handle</I ></TT > should be the value returned by the create function.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-GET">cyg_cpuload_get</H2 ><P >This function returns the latest measurements.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void cyg_cpuload_get(cyg_handle_t handle, cyg_uint32 *average_point1s, cyg_uint32 *average_1s, cyg_uint32 *average_10s);</PRE ></TD ></TR ></TABLE ><P ><TT CLASS="PARAMETER" ><I >handle</I ></TT > should be the value returned by the create function. The load measurements for the last 100ms, 1s and 10s are returned in <TT CLASS="PARAMETER" ><I >*average_point1s</I ></TT >,<TT CLASS="PARAMETER" ><I >*average_1s</I ></TT > and <TT CLASS="PARAMETER" ><I >*average_10s</I ></TT > respectively.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="SERVICES-CPULOAD-API-IMPLEMENTATION">Implementation details</H2 ><P >This section gives a few details of how the measurements are made. This should help to understand what the results mean.</P ><P >When there are no other threads runnable, eCos will execute the idle thread. This thread is always runnable and uses the lowest thread priority. The idle thread does little. It is an endless loop which increments the variable, <TT CLASS="LITERAL" >idle_thread_loops</TT > and executes the macro <TT CLASS="LITERAL" >HAL_IDLE_THREAD_ACTION</TT >. The cpu load measurement code makes use of the variable. It periodically examines the value of the variable and sees how much it has changed. The idler the system, the more it will have incremented. From this it is simple to determine the load of the system.</P ><P >The function <TT CLASS="LITERAL" >cyg_cpuload_calibrate</TT > executes the idle thread for 100ms to determine how much <TT CLASS="LITERAL" >idle_thread_loops</TT > is incremented on a system idle for 100ms. <TT CLASS="LITERAL" >cyg_cpuload_create</TT > starts an alarm which every 100ms calls an alarm function. This function looks at the difference in <TT CLASS="LITERAL" >idle_thread_loops</TT > since the last invocation of the alarm function and so calculated how idle or busy the system has been. The structure <TT CLASS="LITERAL" >cyg_cpuload</TT > is updated during the alarm functions with the new results. The 100ms result is simply the result from the last measurement period. A simple filter is used to average the load over a period of time, namely 1s and 10s. Due to rounding errors, the 1s and 10s value will probably never reach 100% on a fully loaded system, but 99% is often seen.</P ><P >As stated above, clever power management code will interfere with these measurements. The basic assumption is that the idle thread will be executed un-hindered and under the same conditions as when the calibration function was executed. If the CPU clock rate is reduced, the idle thread counter will be incremented less and so the CPU load measurements will give values too high. If the CPU is halted entirely, 100% cpu load will be measured.</P ></DIV ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="services-cpuload.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="services-profile-gprof.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >CPU load measurements</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="services-cpuload.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Application profiling</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
Go to most recent revision | Compare with Previous | Blame | View Log