BogoMIPSValueTooLow < DULG

%SECTION0{name=BogoMIPSValueTooLow}% <nop>BogoMIPS Value too low 

   Question:: We are only seeing 263.78 bogomips on a MPC5200 running
     at 396 MHz. %BR%
     Doesn't this seem way to low ?? With a 603e core I'd expect
     1 bogomip per MHz or better.

   Answer:: No, the values you see is correct.
     Please keep in mind that there is a good reason for the name <strong>Bogo</strong>MIPS. %BR% %BR%
     On [[PowerPC][Power Architecture]]®, the bogomips calculation is measuring the speed of a =dbnz= instruction.
     On some processors like the MPC8xx it takes 2 clocks per =dbnz= instruction,
     and you get 1 <nop>BogoMIP/MHz.
     The MPC5200 takes 3 clocks per =dbnz= in this loop, so you get .67 <nop>BogoMIP/MHz. %BR% %BR%
     See also [[http://tldp.org/HOWTO/BogoMips/bogo-faq.html][The frequently asked questions about BogoMips]]
     (note: this document is somewhat outdated).

   Question:: But I have a MPC8572 running at 1.5GHz, amd it shows only 150 bogomips.
     This cannot be correct?
   Answer:: This value is indeed correct.
     %BR%
     "With recent kernels, when build with ARCH=powerpc, we now use the
     hardware timebase instead of bogus processor loops for short timings.
     Thus our bogomips value is no longer the speed at which the processor
     runs empty loops, but the actual processor timebase value as obtained
     after calibration at boot. " - Benjamin Herrenschmidt

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