* BogoMIPS on 8xx vs 82xx
@ 2003-03-24 7:17 Wojciech Kromer
0 siblings, 0 replies; 2+ messages in thread
From: Wojciech Kromer @ 2003-03-24 7:17 UTC (permalink / raw)
To: Linuxppc-Embedded (E-mail)
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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* RE: BogoMIPS on 8xx vs 82xx
@ 2003-03-24 18:03 Jean-Denis Boyer
0 siblings, 0 replies; 2+ messages in thread
From: Jean-Denis Boyer @ 2003-03-24 18:03 UTC (permalink / raw)
To: Wojciech Kromer; +Cc: Linuxppc-Embedded (E-mail)
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,
--------------------------------------------
Jean-Denis Boyer, B.Eng., Technical Leader
Mediatrix Telecom Inc.
4229 Garlock Street
Sherbrooke (Québec)
J1L 2C8 CANADA
(819)829-8749 x241
--------------------------------------------
> -----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???
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
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