Ricardo,
Jaap-Jan,
quoted
I would expect the bogomips number
to be somewhere near the core clock
(like 8xx).
Well, I think the numbers are pretty fair, assuming that the
bogomips number
reflect a certain amount of external memory accesses at 66
MHz external bus
clock.
It has more to do with pipelining!
Hopefully, there ain't any memory access during calibration...
(except, of course, when the instruction cache is disabled!)
I didn't look at the documentation, but the execution of a branch probably occurs later in the pipeline of a 8260 than for the 860. It probably looses one more cycle. The calibration relies on the execution speed of function __delay (arch/ppc/kernel/misc.S), which loops on a branch instruction 'bdnz'.
Fortunately, the number of bogomips will increase linearly with the core clock.
(These are approximations)
For 8260:
200MHz => 66M bdnz per second => 133BogoMips
266 => 88M => 176
400 => 133M => 266
For 860:
50MHz => 25M bdnz per second => 50BogoMips
Regards,
--------------------------------------------
Jean-Denis Boyer, Eng.
M5T Centre d'Excellence en Télécoms Inc.
4283 Garlock Street
Sherbrooke (Québec)
J1L 2C8 CANADA
(819)829-3972 x241
--------------------------------------------
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
Hello Jean-Denis,
Monday, December 08, 2003, 6:11:30 PM, you wrote:
JDB> Ricardo,
JDB> Jaap-Jan,
quoted
quoted
I would expect the bogomips number
to be somewhere near the core clock
(like 8xx).
Well, I think the numbers are pretty fair, assuming that the
bogomips number
reflect a certain amount of external memory accesses at 66
MHz external bus
clock.
JDB> It has more to do with pipelining!
JDB> Hopefully, there ain't any memory access during calibration...
JDB> (except, of course, when the instruction cache is disabled!)
JDB> I didn't look at the documentation, but the execution of a branch probably occurs later in the pipeline of a 8260 than for the 860. It probably looses one more cycle. The calibration relies on
JDB> the execution speed of function __delay (arch/ppc/kernel/misc.S), which loops on a branch instruction 'bdnz'.
Ooops, I should learn to read the source code before making any
assumptions. Sorry for the mistake, and many thanks for the lesson!
-Scop.
JDB> Regards,
JDB> --------------------------------------------
JDB> Jean-Denis Boyer, Eng.
JDB> M5T Centre d'Excellence en Télécoms Inc.
JDB> 4283 Garlock Street
JDB> Sherbrooke (Québec)
JDB> J1L 2C8 CANADA
JDB> (819)829-3972 x241
JDB> --------------------------------------------
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
On 8-dec-03, at 22:11, Jean-Denis Boyer wrote:
Ricardo,
Jaap-Jan,
quoted
quoted
I would expect the bogomips number
to be somewhere near the core clock
(like 8xx).
Well, I think the numbers are pretty fair, assuming that the
bogomips number
reflect a certain amount of external memory accesses at 66
MHz external bus
clock.
It has more to do with pipelining!
Hopefully, there ain't any memory access during calibration...
(except, of course, when the instruction cache is disabled!)
I didn't look at the documentation, but the execution of a branch
probably occurs later in the pipeline of a 8260 than for the 860. It
probably looses one more cycle. The calibration relies on the
execution speed of function __delay (arch/ppc/kernel/misc.S), which
loops on a branch instruction 'bdnz'.
Fortunately, the number of bogomips will increase linearly with the
core clock.
(These are approximations)
For 8260:
200MHz => 66M bdnz per second => 133BogoMips
266 => 88M => 176
400 => 133M => 266
For 860:
50MHz => 25M bdnz per second => 50BogoMips
Ok, that's a nice explanation, thanks!
Jaap-Jan
Regards,
--------------------------------------------
Jean-Denis Boyer, Eng.
M5T Centre d'Excellence en Télécoms Inc.
4283 Garlock Street
Sherbrooke (Québec)
J1L 2C8 CANADA
(819)829-3972 x241
--------------------------------------------
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/