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 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/
