On Thu, Dec 24, 2015 at 12:47 PM, Anne & Lynn Wheeler <[email protected]> wrote: > <deleted> > risc has been doing cache miss compensation for decades, out-of-order > execution, branch prediction, speculative execution, hyperthreading ... > can be viewed as hardware analogy to 60s multitasking ... given the > processor something else to do while waiting for cache miss. Decade or > more ago, some of the other non-risc chips started moving to hardware > layer that translated instructions into risc micro-ops for scheduling > and execution ... largely mitigating performance difference between > those CISC architectures and RISC. > <deleted> > > as an aside, 370/195 pipeline was doing out-of-order execution ... but > didn't do branch proediction or speculative execution ... and > conditional branch would drain the pipeline. careful coding could keep > the execution units busy getting 10MIPS ... but normal codes typically > ran around 5MIPS (because of conditional branches). I got sucked into > helping with hyperthreading 370/195 (which never shipped), it would > simulate two processors with two instructions streams, sets of > registers, etc ... assuming two instruction streams, each running at > 5MIPS would then keep all execution units running at 10MIPS. > <deleted> > > -- > virtualization experience starting Jan1968, online at home since Mar1970 > https://en.wikipedia.org/wiki/IBM_7030_Stretch First computer to implement: Multiprogramming, memory protection, generalized interrupts, the eight-bit byte, instruction pipelining, prefetch and decoding, and memory interleaving.
If branch predicting is a big hang up, the obvious solution is to start processing all possible outcomes then keep the one that is actually taken. I. E. B OUTCOME(R15) where R15 is a return code of 0,4,8,12,16. -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
