On 8-dec-03, at 22:11, Jean-Denis Boyer wrote: > > Ricardo, > Jaap-Jan, > >>> 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 T?l?coms Inc. > 4283 Garlock Street > Sherbrooke (Qu?bec) > J1L 2C8 CANADA > (819)829-3972 x241 > -------------------------------------------- ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/