Hello Joerg, On Sat, Mar 19, 2005 at 10:29:28PM +0000, Joerg Sommer wrote: > Benjamin Herrenschmidt <[EMAIL PROTECTED]> wrote: > > On Mon, 2005-03-14 at 16:01 +0000, Jochen Voss wrote: > > > >> From other people's posts I conclude that bogomips should approximately > >> equal clock? > > > > It depends on the CPU, but on a 7447A, yes. > > Do you know why it is for i386 nearly the double of cpu clock? Or reverse, > why is it only equal the clock on ppc?
I am no expert on this, but the delay loop in question is _GLOBAL(__delay) cmpwi 0,r3,0 mtctr r3 beqlr 1: bdnz 1b blr in file "arch/ppc/kernel/misc.S". I do not yet speak powerpc assembler, but I read bdnz as decrease (register r3?) and branch backwards to label 1 if the result is not zero. Probably a 7447A CPU can do this within 1 CPU clock cycle? I didn't check the loop for i386 but maybe it consists of two instructions or of one which takes two CPU clock cycles? I hope this helps, Jochen PS.: Probably the "MPC7450 RISC Microprocessor Family Reference Manual" (downloadable from [1]) contains the timing information for the MPC7447A processor, but it is hard stuff to understand after midnight. [1] http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPC7447A&nodeId=018rH3bTdG8653 -- http://seehuhn.de/
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