Thread (8 messages) 8 messages, 6 authors, 2008-11-26

Re: too few bogoMips on MPC8313E-RDB ?

From: Alessandro Rubini <hidden>
Date: 2008-11-26 10:33:31

This is what a linux-2.6.x reports (for the MPC8313E running at 333 MHz):
Calibrating delay loop... 83.20 BogoMIPS (lpj=166400)

Which can't be correct.

A MPC870 (running at 133 mhz) has ~ 131.07 BogoMIPS
Actaully, one-instruction-per-clock leads to BogoMIPS = MHz.

Your "loop per jiffies" value shows you make 332800 instructions per
jiffy (a loop is two instructions: increment and jump).

So most liker your timer tick runs at 1000 Hz but Linux is thinking
it's at 250Hz (332800 * 250 = 83.20 millions).
Of course it's only a benchmark figure.
No, it's not a benchmark figure. It's the metric by which udelay() is
calculated. So your udelays (and mdelays) will be 4 times shorter than
required, and some hardware may be misbehaving as a result.

Hope this help
/alessandro, who however is not runing a powerPC these times
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