BogoMIPS change in 3.6+

The BogoMIPS value has changed on highbank since the commit below in 3.6. It is now half the value it used to be. Does that matter other than perception (I've checked that I'm not running at half the freq)?

Rob

commit d0a533b18235d36206b9b422efadb7cee444dfdb

Author: Will Deacon <[email protected]>
Date:   Fri Jul 6 15:47:17 2012 +0100

ARM: 7452/1: delay: allow timer-based delay implementation to be
selected

This patch allows a timer-based delay implementation to be selected by switching the delay routines over to use get_cycles, which is implemented in terms of read_current_timer. This further allows us to skip the loop calibration and have a consistent delay function in the face of core frequency scaling.

To avoid the pain of dealing with memory-mapped counters, this implementation uses the co-processor interface to the architected timers when they are available. The previous loop-based implementation is kept around for CPUs without the architected timers and we retain both the maximum delay (2ms) and the corresponding conversion factors for determining the number of loops required for a given interval. Since the indirection of the timer routines will only work when called from C, the sa1100 sleep routines are modified to branch to the loop-based delay functions directly.

I think the only danger is that your customers might think they are running at half the clock rate. Nothing in the kernel should be using the BogoMIPS value.

Arnd

Hi Rob,

Are you registering a delay timer? If not, then the delay loop should be identical to what it was before, so that's certainly a surprise...

Are your delays ballpark correct (try 2ms)?

Will

Yes, the delays are correct and this is an A9. So I guess this may be a surprise, but seems it is a non-issue. I'm sure I'll be getting asked about this...

Rob

I also stumbled on this while testing Will's series.[1] There should be no other functional issue apart from getting surprised.

Regards,
Santosh

[1]
http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/109281.html

Right, but you were using the arch-timers w/ Cortex-A15. I thought Highbank was A9?

Will

Ahh.. Sorry looking at description I just thought it could be the same issue.

Regards,
Santosh