目前有多种在嵌入式计算机操作系统中检测CPU占用率的方法，例如，目前在嵌入式操作系统vxWorks中主要有两种CPU占用率检测的方法。
第一种：通过spy工具利用辅助定时器产生中断，并且为每个任务维护一个计数器。然后记下被中断的任务，并且将该任务的计数器加一。经过一段时间后，每个任务的计数器反映了该任务占用CPU利用率的情况。很明显，这是利用抽样技术。并且得到的cpu利用率的准确程度取决于任务的持续性和周期性。
通过查找spyLib.h的文件，我们发现除了spy()函数外，还有一spyCommon函数,带一函数指针参数。推测函数指针类型为（int）（*p）(char * fmtStr,…)（经过验证确实如此）。所以可以写一自己的函数去接受spy需要打印的数据，Spy调用该函数按行打印结果。我们可以不断分析一行字符串来得到我们需要的结果。
int SpyPtnFunc(const char * fmtPtn,...)
{
char buf[128];
CPUUSAGEDATAMSG data;
va_list vl;
va_start(vl,fmtPtn);
vsprintf(buf,fmtPtn,vl); //得到一行字符串。
va_end(vl);
//分析buf,得到一个任务的CPU的使用情况。
return 0;
}
第二种：通过创建两个特殊的任务，一个优先级别最高的任务和一个优先级别最低的任务，在这个优先级别最高的任务里运行一个循环次数很大的循环用于占用所有的CPU时间，记录一段时间内计数值；然后再设置一个优先级别最低的任务，当所有任务都停止时CPU才会调度此任务，此任务记下在无其他任务占用CPU的情况下计数，最后通过算法CPU占用率 = （total -idle）% total。
但这两种算法都需要硬件系统配备相应高精度的辅助时钟，为了节约成本，通常没有这样的时钟，相对第一种方法来说，精确计算各任务CPU占用率没有必要，作为报警需要，计算系统总的CPU占用率即可；第二种虽然是计算整个系统的占用率，但必须需要硬件时钟的中断才能实现。
第二种方法的另一种解释是： 利用一特殊任务，该任务的优先级比系统中的所有任务的优先级都低，该任务是死循环，该任务的目的就是消耗cpu资源，占用cpu空闲时间，因为当系统中其它任务都被挂其时，该任务才能得到cpu的使用权。假设一段时间total内，该任务的运行时间为idle，cpu利用率的计算公式为（total-idle）%total。这一种方法实现起来很简单，但是它只能算得整个系统的cpu使用情况，不能得到单个任务的cpu使用情况！同时它会使cpu满负荷工作。源代码如下
#include "VxWorks.h"
#include "semLib.h"
#include "taskLib.h"
#define SECONDS_TO_BURN 60
typedef struct cpuUsage {
SEM_ID startSem;
int didNotComplete;
unsigned long ticksNoContention;
int nBurnNoContention;
unsigned long ticksNow;
int nBurnNow;
double usage;
} cpuUsage;
static cpuUsage *pcpuUsage=0;
static double cpuBurn()
{
int i;
double result = 0.0;
for(i=0;i<5; i++) result += sqrt((double)i);
return(result);
}
static void cpuUsageTask()
{
while(TRUE) {
int i;
unsigned long tickStart,tickEnd;
semTake(pcpuUsage->startSem,WAIT_FOREVER);
pcpuUsage->ticksNow=0;
pcpuUsage->nBurnNow=0;
tickStart = tickGet();
for(i=0; i< pcpuUsage->nBurnNoContention; i++) {
cpuBurn();
pcpuUsage->ticksNow = tickGet() - tickStart;
++pcpuUsage->nBurnNow;
}
tickEnd = tickGet();
pcpuUsage->didNotComplete = FALSE;
pcpuUsage->ticksNow = tickEnd - tickStart;
}
}
double getCpu()
{
if(pcpuUsage->didNotComplete && pcpuUsage->nBurnNow==0) {
pcpuUsage->usage = 0.0;
} else {
double temp;
double ticksNow,nBurnNow;
ticksNow = (double)pcpuUsage->ticksNow;
nBurnNow = (double)pcpuUsage->nBurnNow;
ticksNow *= (double)pcpuUsage->nBurnNoContention/nBurnNow;
temp = ticksNow - (double)pcpuUsage->ticksNoContention;
temp = 100.0 * temp/ticksNow;
if(temp100.0) temp=0.0; /*handle tick overflow*/
pcpuUsage->usage = temp;
}
pcpuUsage->didNotComplete = TRUE;
semGive(pcpuUsage->startSem);
printf("CPU usage:%f/r/n",pcpuUsage->usage);
return(pcpuUsage->usage);
}
void cpuUsageInit(void)
{
unsigned long tickStart,tickNow;
int nBurnNoContention=0;
int ticksToWait;
ticksToWait = SECONDS_TO_BURN*sysClkRateGet();
pcpuUsage = calloc(1,sizeof(cpuUsage));
tickStart = tickGet();
/*wait for a tick*/
while(tickStart==(tickNow = tickGet())) {;}
tickStart = tickNow;
while(TRUE) {
if((tickGet() - tickStart)>=ticksToWait) break;
cpuBurn();
nBurnNoContention++;
}
pcpuUsage->nBurnNoContention = nBurnNoContention;
pcpuUsage->startSem = semBCreate (SEM_Q_FIFO,SEM_EMPTY);
pcpuUsage->ticksNoContention = ticksToWait;
pcpuUsage->didNotComplete = TRUE;
taskSpawn("cpuUsageTask",255,VX_FP_TASK,1000,(FUNCPTR)cpuUsageTask, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
}
VxWorks cpu utilization(spy command)
% spyHelp
spyHelp Print this list
spyClkStart [ticksPerSec] Start task activity monitor running at ticksPerSec ticks per second
spyClkStop Stop collecting data
spyReport Prints display of task activity statistics
spyStop Stop collecting data and reports
spy [freq[,ticksPerSec]] Start spyClkStart and do a report [every "freq" second ]
* spyReport - display task activity data
*
* This routine reports on data gathered at interrupt level for the amount of
* CPU time utilized by each task, the amount of time spent at interrupt level,
* the amount of time spent in the kernel, and the amount of idle time. Time
* is displayed in ticks and as a percentage, and the data is shown since both
* the last call to spyClkStart() and the last spyReport(). If no interrupts
* have occurred since the last spyReport(), nothing is displayed.
*
* RETURNS: N/A
*
* SEE ALSO: spyLib, spyClkStart(),
* .pG "Target Shell"
% spyReport NAME ENTRY TID PRI total % (ticks) delta % (ticks) -------- -------- ----- --- --------------- --------------- tExcTask excTask 2f788870 0 0% ( 0) 0% ( 0) tLogTask logTask 2f7807a0 0 0% ( 0) 0% ( 0) DebugDaemon 2e64abd0 21 0% ( 0) 0% ( 0) MsTimer_task 2e6b22f0 29 0% ( 0) 0% ( 0) CpuUsageTask Get_Cpu_Us 2f432560 40 0% ( 0) 0% ( 0) ipcom_tickd 2e5e0ef0 40 0% ( 0) 0% ( 0) tNetTask netTask 2f434fa0 50 0% ( 1) 0% ( 1) monitor monitorTas 2eda2880 50 0% ( 0) 0% ( 0) timer_util 2e6efb60 51 0% ( 0) 0% ( 0) tPortmapd portmapd 2edaeeb0 54 0% ( 0) 0% ( 0) ifa_Prt 69f4ff0 58 0% ( 0) 0% ( 0) DmmListenTas 2e69ac50 60 0% ( 0) 0% ( 0) DmmSendTask 2e6aa610 61 0% ( 0) 0% ( 0) DmmRecvTask 2e6a2930 61 0% ( 0) 0% ( 0) ipcom_syslog 2e60da20 70 0% ( 0) 0% ( 0) ipsshd ipssh 2e5e5130 70 0% ( 0) 0% ( 0) cps 7f70460 81 0% ( 0) 0% ( 0) cpa 7f39670 81 0% ( 0) 0% ( 0) phyStatus phyStatusC 2eda6650 100 0% ( 0) 0% ( 0) tTftpdTask tftpdTask 2e6ffb40 100 0% ( 0) 0% ( 0) tHwm 2ff42ae0 101 0% ( 0) 0% ( 0) gfm 7f510e0 101 0% ( 0) 0% ( 0) HWM_socket 6eb1e20 101 0% ( 0) 0% ( 0) SDD_1HZInt sdd_1HZInt 2ffbe810 106 0% ( 0) 0% ( 0) SFT_CheckTas 2e68b0c0 131 0% ( 0) 0% ( 0) SFT_SwitchTa 2e682ed0 131 0% ( 0) 0% ( 0) te_schdl 78a30a0 160 0% ( 0) 0% ( 0) DmmLinkCtrlT 2e692f70 166 0% ( 0) 0% ( 0) ppp_ctl 7ed5930 170 0% ( 0) 0% ( 0) Ipinip Ipinip_Tas 6868e80 170 0% ( 0) 0% ( 0) IpTunnel IpTunnel_T 36c2f40 170 0% ( 0) 0% ( 0) OsiLight OsiLight 3879370 170 0% ( 0) 0% ( 0) DALLAS_OVERF 7f02c50 171 0% ( 0) 0% ( 0) ppp_rcv 7ee6370 171 0% ( 0) 0% ( 0) ppp_snd 7ec4ef0 171 0% ( 0) 0% ( 0) TM_daemon 2e89e660 179 0% ( 0) 0% ( 0) AmmBringUpTa 2e652b20 179 0% ( 0) 0% ( 0) DCC_IF 2ffb3db0 180 0% ( 0) 0% ( 0) DCC 2ffa3240 180 0% ( 0) 0% ( 0) ccs 7fae0a0 180 0% ( 0) 0% ( 0) tFtpdTask 6ed6060 180 0% ( 0) 0% ( 0) tDtlRecvMsg dtl_socket 2e8694c0 181 0% ( 0) 0% ( 0) tSnmp 2ff926d0 181 0% ( 0) 0% ( 0) GCB 2ff62320 181 0% ( 0) 0% ( 0) GCM 2ff5a510 181 0% ( 0) 0% ( 0) GRM 2ff52700 181 0% ( 0) 0% ( 0) cli 7f0a930 181 0% ( 0) 0% ( 0) cli_console 6d10710 181 0% ( 0) 0% ( 0) GCB_socket_t 6863e20 181 0% ( 0) 0% ( 0) GCB_TSB_sock 685bfe0 181 0% ( 0) 0% ( 0) tAgentX snmpAgentX 6847790 181 0% ( 0) 0% ( 0) GMSL1 66c9510 181 0% ( 0) 0% ( 0) GMSL2 3e94db0 181 0% ( 0) 0% ( 0) tPsm_Sync 66932d0 191 0% ( 0) 0% ( 0) rpr_rpm 7f21fd0 200 0% ( 0) 0% ( 0) tSnmpTmr timerTask 6cf4740 200 0% ( 0) 0% ( 0) pcm 2ff0f840 201 0% ( 0) 0% ( 0) spm 7f68780 201 0% ( 1) 0% ( 1) ccs_mib 6d3bea0 210 0% ( 0) 0% ( 0) fmm_LedPolli 69c4b00 210 0% ( 0) 0% ( 0) fmm_SendAlar 69b63e0 210 0% ( 0) 0% ( 0) fmm_ProcessA 69ae700 210 0% ( 0) 0% ( 0) SFT_SynTask 2e67afe0 221 0% ( 0) 0% ( 0) SFT_PollTask 2e6730f0 221 0% ( 0) 0% ( 0) SDD_Slot_Mon sdd_SlotSe 2ffbbd90 221 0% ( 0) 0% ( 0) SDD_Slot_Pol sdd_slotPo 2ffb9310 221 0% ( 0) 0% ( 0) cmi 7fd8d70 221 0% ( 0) 0% ( 0) cmc 7fd1090 221 0% ( 0) 0% ( 0) cpc 7f78140 221 0% ( 0) 0% ( 0) pm_manager 7fffdd0 226 0% ( 0) 0% ( 0) pm_agent 7ff80f0 226 0% ( 0) 0% ( 0) fma_agent 7ff0410 226 0% ( 0) 0% ( 0) fm_convert 7fb5d80 226 0% ( 0) 0% ( 0) ifa 7f95980 228 0% ( 0) 0% ( 0) cad 7fc6ca0 230 0% ( 0) 0% ( 0) ifm 7f87b00 230 0% ( 0) 0% ( 0) tTffsPTask flPollTask 2f77e9c0 231 0% ( 0) 0% ( 0) tMibMgr 2e663230 231 0% ( 0) 0% ( 0) tMibRmt 2e65aad0 231 0% ( 0) 0% ( 0) tLcm 2ff71f40 231 0% ( 0) 0% ( 0) lea 2ff3abf0 231 0% ( 0) 0% ( 0) lem 2ff32de0 231 0% ( 0) 0% ( 0) cfa 2ff2afd0 231 0% ( 0) 0% ( 0) tod 2ff231c0 231 0% ( 0) 0% ( 0) tmi 7fe8730 231 0% ( 0) 0% ( 0) cai 7fe0a50 231 0% ( 0) 0% ( 0) fm_mgr 7fbefc0 231 0% ( 0) 0% ( 0) m4m 7fa63c0 231 0% ( 0) 0% ( 0) oam 7f7fe20 231 0% ( 0) 0% ( 0) Msm 7f60aa0 231 0% ( 0) 0% ( 0) mpm 7f58dc0 231 0% ( 0) 0% ( 0) cpm 7f41350 231 0% ( 0) 0% ( 0) epm 7f31990 231 0% ( 0) 0% ( 0) UDM 7f29cb0 231 0% ( 0) 0% ( 0) prbs_manager 7f1a2f0 231 0% ( 0) 0% ( 0) c80_s 7f12610 231 0% ( 0) 0% ( 0) tMibRmt1 6ef4a00 231 0% ( 0) 0% ( 0) tMibRmt2 6eecd20 231 0% ( 0) 0% ( 0) tCfCardPoll cfCardPoll 69daa80 231 0% ( 0) 0% ( 0) tod_SCP tod_System 69d8130 231 0% ( 0) 0% ( 0) tmi_MsgTask 666ee50 231 0% ( 0) 0% ( 0) SDD sdd_PollTa 2ffc3b80 232 1% ( 5) 1% ( 5) tUpgrade 2ff81b60 232 0% ( 0) 0% ( 0) tMfm 2ff79d50 232 0% ( 0) 0% ( 0) tFtm 2ff6a130 232 0% ( 0) 0% ( 0) tTrap 7878890 232 0% ( 0) 0% ( 0) m4m_socket 69a6a20 232 0% ( 0) 0% ( 0) trap_dest_1 trapWorkTa 34bfda0 232 0% ( 0) 0% ( 0) trap_dest_2 trapWorkTa 34aca10 232 0% ( 0) 0% ( 0) ael_EventMsg 66d11f0 235 0% ( 0) 0% ( 0) SDD_CardPre sdd_Pollin 2ffb6890 236 0% ( 0) 0% ( 0) ael 2ff1b3b0 236 0% ( 0) 0% ( 0) cmi_Poll 7849ea0 236 0% ( 0) 0% ( 0) lea_LedPolli 69e2760 236 0% ( 0) 0% ( 0) slowJOB slowJobTas 2f72efb0 238 0% ( 0) 0% ( 0) slowJOB2 slowJobTas 2f72c570 238 0% ( 0) 0% ( 0) pinger 7516180 238 0% ( 0) 0% ( 0) fmc_DefectPr fmc_Defect 6ab88a0 238 14% ( 44) 14% ( 44) fma_DefectPr fma_Defect 69f8cd0 238 0% ( 0) 0% ( 0) ifa_Poll 69eb9a0 238 0% ( 0) 0% ( 0) tPsm 2ff4a8f0 241 0% ( 0) 0% ( 0) tMibSaver 6ed2380 241 0% ( 0) 0% ( 0) tGCM_Save 6d074d0 241 0% ( 0) 0% ( 0) tGCM_Test_St 6cff7f0 241 0% ( 0) 0% ( 0) tPsm_Backup 6727480 241 0% ( 0) 0% ( 0) tPsm_Save 671f7a0 241 0% ( 0) 0% ( 0) tDcacheUpd dcacheUpd 2e610a10 250 0% ( 0) 0% ( 0) Pmm_WriteFil 6ab4bc0 250 0% ( 0) 0% ( 0) Pmm_WritexSe 6aacee0 250 0% ( 0) 0% ( 0) tDtlPrintMsg dtl_PrintP 2e71a870 251 6% ( 18) 6% ( 18) SFT_FileTask 2e66b120 251 12% ( 36) 12% ( 36) tDtldmmMsg 2e642c20 251 0% ( 0) 0% ( 0) ael_LogTask 66dcc30 251 0% ( 0) 0% ( 0) tPbPrint printTask 2f7898c0 252 0% ( 0) 0% ( 0) security_log 6eca6a0 253 0% ( 1) 0% ( 1) StackCheck 2e717c60 254 0% ( 1) 0% ( 1) trapTest 786d030 254 0% ( 0) 0% ( 0) Idle 2e70fe50 255 63% ( 187) 63% ( 187) KERNEL 0% ( 1) 0% ( 1) INTERRUPT 0% ( 0) 0% ( 0) IDLE 0% ( 0) 0% ( 0) TOTAL
