Re: DIfferent BogoMIPS value after bbaa06702719 ("clocksource/drivers/arm_global_timer: Register delay timer")

From: RafaÅ MiÅecki
Date: Thu Mar 02 2017 - 15:31:22 EST


On 03/02/2017 03:13 PM, Russell King - ARM Linux wrote:
On Thu, Mar 02, 2017 at 02:36:23PM +0100, RafaÅ MiÅecki wrote:
Hi,

I just updated kernel on my SmartRG SR400ac (bcm4708-smartrg-sr400ac.dts) from
4.4 to 4.9 and noticed that this part of the log:
[ 0.020820] Calibrating delay loop... 1594.16 BogoMIPS (lpj=7970816)
(...)
[ 0.190806] Brought up 2 CPUs
[ 0.200022] SMP: Total of 2 processors activated (3188.32 BogoMIPS).

became:
[ 0.027082] Calibrating delay loop (skipped), value calculated using timer frequency.. 800.00 BogoMIPS (lpj=4000000)
(...)
[ 0.078858] Brought up 2 CPUs
[ 0.088254] SMP: Total of 2 processors activated (1600.00 BogoMIPS).

This is caused by commit bbaa06702719 ("clocksource/drivers/arm_global_timer:
Register delay timer").

Is this something expected?

Yes.

Or should I be worried about this? I'm aware it's just BogoMIPS, but I
still prefer to ask :)

It's *bogus*. Bogomips is the calibration value that the kernel uses
to achieve delays. It has nothing to do with the speed of the CPU on
modern systems that use a timer instead. (In that case, it's a
calibration value for the timer, rather than a calibration value for
the number of software loops required to achieve a delay.)

Now I can sleep calm ;) thanks!