Accurate calculation of CPU usage given in percentage in Linux?

by

According the htop source code, my assumptions looks like they are valid:

(see static inline double LinuxProcessList_scanCPUTime(LinuxProcessList* this) function at LinuxProcessList.c)

// Guest time is already accounted in usertime
usertime = usertime - guest;                             # As you see here, it subtracts guest from user time
nicetime = nicetime - guestnice;                         # and guest_nice from nice time
// Fields existing on kernels >= 2.6
// (and RHEL's patched kernel 2.4...)
unsigned long long int idlealltime = idletime + ioWait;  # ioWait is added in the idleTime
unsigned long long int systemalltime = systemtime + irq + softIrq;
unsigned long long int virtalltime = guest + guestnice;
unsigned long long int totaltime = usertime + nicetime + systemalltime + idlealltime + steal + virtalltime;

And so, from fields listed in the first line of /proc/stat: (see section 1.8 at documentation)

     user    nice   system  idle      iowait irq   softirq  steal  guest  guest_nice
cpu  74608   2520   24433   1117073   6176   4054  0        0      0      0

Algorithmically, we can calculate the CPU usage percentage like:

PrevIdle = previdle + previowait
Idle = idle + iowait

PrevNonIdle = prevuser + prevnice + prevsystem + previrq + prevsoftirq + prevsteal
NonIdle = user + nice + system + irq + softirq + steal

PrevTotal = PrevIdle + PrevNonIdle
Total = Idle + NonIdle

# differentiate: actual value minus the previous one
totald = Total - PrevTotal
idled = Idle - PrevIdle

CPU_Percentage = (totald - idled)/totald

More Related Contents:

  1. create a file with prefix =file1 followed by the random number
  2. How do the likely/unlikely macros in the Linux kernel work and what is their benefit?
  3. What happens to an open file handle on Linux if the pointed file gets moved or deleted
  4. How to get overall CPU usage (e.g. 57%) on Linux [closed]
  5. Finding which process was killed by Linux OOM killer [closed]
  6. How to debug the Linux kernel with GDB and QEMU?
  7. Use of floating point in the Linux kernel
  8. Whole one core dedicated to single process
  9. Handling multiple SIGCHLD
  10. kernel stack and user space stack
  11. How to mmap a Linux kernel buffer to user space?
  12. Using gdb to single-step assembly code outside specified executable causes error “cannot find bounds of current function”
  13. How to continuously monitor the directory using dnotify /inotify command
  14. How to create a CPU spike with a bash command
  15. What is the interface for ARM system calls and where is it defined in the Linux kernel?
  16. How does Linux determine the next PID?
  17. How to add poll function to the kernel module code?
  18. How to obtain the number of CPUs/cores in Linux from the command line?
  19. How to access(if possible) kernel space from user space?
  20. Do Kernel pages get swapped out?
  21. How to avoid transparent_hugepage/defrag warning from mongodb?
  22. Converting jiffies to milli seconds
  23. Direct Memory Access in Linux
  24. Linux Stack Sizes
  25. How to decode /proc/pid/pagemap entries in Linux?
  26. init function invocation of drivers compiled into kernel
  27. Signed executables under Linux
  28. How can I monitor the NIC status(up/down) in a C program without polling the kernel?
  29. How can I create a device node from the init_module code of a Linux kernel module?
  30. Sending UDP packets from the Linux Kernel

Leave a Comment