[ELDK] Bogomips difference between 2.6.25 and 2.6.30

[Philippe Villet]

Dear Wolfgang,

If I force the timer clock to be CPU clock (By setting the 3 parameter to zero) :
ibm440ep_fixup_clocks(sysclk, 0, 0);
I get ;
Calibrating delay loop... 790.52 BogoMIPS (lpj=1581056)
In this case I confirm that :
timebase = clock = bogomips / 2
But I want to use the TMRCLK input clock (25MHz on my custom board), so I wrote :
ibm440ep_fixup_clocks(sysclk, 0, 25000000);
and got :
Calibrating delay loop... 49.92 BogoMIPS (lpj=99840)

I've checked the timebase_period_ns variable defined in devtree.c, generic_calibrate_decr function in time.c and everything seems correct.

Any idea?
Thanks.

Philippe

-----Message d'origine-----
De : Wolfgang Denk [mailto:wd at denx.de] 
Envoyé : vendredi 4 septembre 2009 17:24
À : Philippe Villet
Cc : eldk at lists.denx.de
Objet : Re: [ELDK] Bogomips difference between 2.6.25 and 2.6.30

Dear "Philippe Villet",

In message <F9D1A9212590B640B744B50EF9E01686044E130C at ENIEXCH01.ds.jdsu.net> you wrote:
> 
> On our custom board (based on AMCC 440EPx) , we have 592 Bogomips with a
> 2.6.25 kernel and only 50 bogomips with a 2.6.30 (moving from a ppc to
> powerpc architecture).
> 
> Is there any reason for such a difference?????

Do you just see such a difference in the bogmips numbers, or also in
the real system performance?

> /proc/cpuinfo on 2.3.30
> processor       : 0
> cpu             : 440EPX
> clock           : 396.200004MHz
> revision        : 24.212 (pvr 2162 18d4)
> bogomips        : 49.92
> timebase        : 25000000
> platform        : PowerPC 44x Platform
> model           : jdsu,mts4000
> Memory          : 255 MB

Where is the difference between clock and timebase coming from?
Normally we see timebase = clock = bogomips / 2.



I cannot confirm such behaviour from our systems; just tested out
current development kernel (v2.6.31-rc8-1360-g39b19e6) on two Sequoia
boards (an old one at 528 MHz and a more recent one at 666 MHz):


U-Boot 2009.06 (Jul 22 2009 - 15:21:57)

CPU:   AMCC PowerPC 440EPx Rev. A at 528 MHz (PLB=132, OPB=66, EBC=66 MHz)
       Security/Kasumi support
       Bootstrap Option H - Boot ROM Location I2C (Addr 0x52)
       Internal PCI arbiter enabled, PCI async ext clock used
       32 kB I-Cache 32 kB D-Cache
Board: Sequoia - AMCC PPC440EPx Evaluation Board, Rev. F, PCI=66 MHz
...
## Booting kernel from Legacy Image at 00400000 ...
   Image Name:   Linux-2.6.31-rc8-01360-g39b19e6
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    1456635 Bytes =  1.4 MB
   Load Address: 00000000
   Entry Point:  00000000
   Verifying Checksum ... OK
...
-bash-3.2# cat /proc/cpuinfo 
processor       : 0
cpu             : 440EPX
clock           : 528.000008MHz
revision        : 24.208 (pvr 2162 18d0)
bogomips        : 1056.00
timebase        : 528000008
platform        : PowerPC 44x Platform
model           : amcc,sequoia
Memory          : 255 MB


And:

CPU:   AMCC PowerPC 440EPx Rev. A at 666.667 MHz (PLB=166, OPB=83, EBC=55 MHz)
       Security/Kasumi support
       Bootstrap Option H - Boot ROM Location I2C (Addr 0x52)
       Internal PCI arbiter enabled, PCI async ext clock used
       32 kB I-Cache 32 kB D-Cache
Board: Sequoia - AMCC PPC440EPx Evaluation Board, Rev. F, PCI=33 MHz
...
## Booting kernel from Legacy Image at 00400000 ...
   Image Name:   Linux-2.6.31-rc8-01360-g39b19e6
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    1456635 Bytes =  1.4 MB
   Load Address: 00000000
   Entry Point:  00000000
   Verifying Checksum ... OK
...
-bash-3.2# cat /proc/cpuinfo 
processor       : 0
cpu             : 440EPX
clock           : 666.666670MHz
revision        : 24.208 (pvr 2162 18d0)
bogomips        : 1333.33
timebase        : 666666670
platform        : PowerPC 44x Platform
model           : amcc,sequoia
Memory          : 255 MB



Best regards,

Wolfgang Denk

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