RE: BogoMIPS on 8xx vs 82xx

The ppc function used in calibration is __delay.
It is located in arch/ppc/kernel/misc.S.
It uses instruction bdnz, looping on itself.
On 860, it takes 2 cycles per bdnz.
On 8260, it takes 3 cycles per bdnz.
I guess it is because both CPUs have different pipelines.
The result is later multiplied by 2 prior to be displayed,
around line 197 in init/main.c.
This is why it gives 1BogoMips = 1MHz on 860.

Regards,
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 Jean-Denis Boyer, B.Eng., Technical Leader
 Mediatrix Telecom Inc.
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-----Original Message-----
From: Wojciech Kromer [mailto:krom@dgt-lab.com.pl]
Sent: 24 mars, 2003 02:17
To: Linuxppc-Embedded (E-mail)
Subject: BogoMIPS on 8xx vs 82xx



On 8xx running 50 MHz gives ~ 50 BogoMIPS, runnig 65 gives
approx 65 and
so on, close to linear...
but on 8250 running core 266Mhz  (66 on bus, 133 cpm) i get only
175BogoMIPS. Why???

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