MPC5200 bogomips
Mark Chambers
markc at mail.com
Fri Jan 28 04:52:32 EST 2005
----- Original Message -----
From: "Stuart Adams" <sja at brightstareng.com>
To: <linuxppc-embedded at ozlabs.org>
Sent: Thursday, January 27, 2005 11:29 AM
Subject: MPC5200 bogomips
>
> We are only seeing 263.78 bogomips on a MPC5200 running
> at 396 MHz.
>
> Doesn't this seem way to low ?? With a 603e core I'd expect
> 1 bogomip per MHz or better.
>
> The exact same kernel source running on an 8xx PPC gets about
> 1 bogomip per MHZ and my 745 CPU board does 2 bogomips
> per MHz ... the bogomip calibration code is the same for all
> PPC architectures so it seem like it should be an apples-to-apples
> comparison.
>
> -- Stuart
>
Ha! You almost sound like you are quoting me from when I first
looked at bogomips on the 5200. Here's the story: If you drill
down to where bogomips are calculated you will see that it is
measuring the speed of a dbnz instruction. The calculation assumes
2 clocks per dbnz. So the 8xx comes out at 1 BogoMIP/MHz. The
5200 takes 3 clocks/dbnz in this loop, so you get .67 BogoMIP/MHz.
Not to worry, it's only one specific scenario. Overall I've found the
5200 to be about 1.5 MIPS/MHz compared to 8xx 1 MIPS/MHz.
Mark Chambers
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