at91sam9260 BogoMIPS

[Sergey Lapin]

Hi, all!
Sorry for dumb question, but I generally used to see BogoMIPS on most
ARM hardware to be equal to CPU speed im MHz, so 200Mhz PXA
is about 200 BogoMIPS. But AT91SAM9260 at 180 MHz (with 90 MHz master clock)
shows only 89 BogoMIPS. Is it normal or I have some misconfiguration somewhere?

Thanks a lot,
S.

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[Marc Pignat]

Post by Sergey Lapin
Hi, all!
Sorry for dumb question, but I generally used to see BogoMIPS on most
ARM hardware to be equal to CPU speed im MHz, so 200Mhz PXA
is about 200 BogoMIPS. But AT91SAM9260 at 180 MHz (with 90 MHz master clock)
shows only 89 BogoMIPS. Is it normal or I have some misconfiguration somewhere?

My at91rm9200 (arm920t) at 180MHz gives me 88.16 BogoMIPS, your AT91SAM9260 is
an arm926 which is similar, so your BogoMIPS seems all right!

My xscale 600 MHz gives me 593.10 BogoMIPS, so the xscale seems run empty loops
faster ;)

Best regards

Marc

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[Martin Krause]

Hi Sergey,

Post by Sergey Lapin
Hi, all!
Sorry for dumb question, but I generally used to see BogoMIPS on most
ARM hardware to be equal to CPU speed im MHz, so 200Mhz PXA
is about 200 BogoMIPS. But AT91SAM9260 at 180 MHz (with 90 MHz master
clock) shows only 89 BogoMIPS. Is it normal or I have some
misconfiguration somewhere?

Maybe you have configured a disadvantageous bus mode. AFAIK ARM9
supports three bus modes: FastBus, asynchronous and synchronous.

Some time ago we had an issue with configuring the wrong bus mode.
In fast bus mode our AT91RM9200 only performed with a third BogoMIPS
compared to asynchronous bus mode. And not only the BogoMIPS
value was a third, also the whole CPU performance (measured with
nbench benchmark).

AFAIK the bus mode is not configured in kernel, but in your boot
firmware. For U-Boot and ARM920T core you could find some
information on the U-Boot mailing list:

http://article.gmane.org/gmane.comp.boot-loaders.u-boot/17046/match=add+csb637+at91rm9200

and here:

http://article.gmane.org/gmane.comp.boot-loaders.u-boot/17033/match=add+csb637+at91rm9200

Best Regards,
Martin Krause

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