Subject: Re: too few bogoMips on MPC8313E-RDB ?

From: Alessandro Rubini <[email-masked]>
Date: Wed, 26 Nov 2008 11:20:42 +0100

> 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