From: Charles Mills <[email protected]> Date: 07/10/2013 11:15 AM
This drifted into a discussion of manual links. Did anyone address > Has anyone done benchmarks on different scenarios with instructions with immediate & relative instructions versus the old instructions My personal opinion are 1. I doubt that the differences are significant unless you are calculating pi to 1000 digits or implementing your own 8192-bit encryption. 2. The relative instructions are SO convenient relative (sorry) to the old base/displacement instructions that I wonder how we ever lived without them. 3. Even if they are a little slower, it would not take very many eliminated "save and load another base register" scenarios to make up for it. 4. Because of pipelining, caching and so forth it is difficult to construct benchmarks that are going to accurately reflect your real-world situation. Charles -------------------------- Amen to 1, 2, and 4. Especially 4. In a past life, working at AMDAHL, we had to use standalone time to run specific loads to do timing determinations. Most companies can't afford to put a machine in basic mode (assuming it were even possible with PR/SM today) for a few hours to do such testing. Until one programs at the level of the machine's "Hypervisor" (what else would you call a Domain/LPAR controller?), one probably does not have an appreciation for all the interrupts that take place (including some that are not in the PoOP manual). This makes it very difficult to get into a deterministic environment to do such timings. And again, with pipelining, cache, out-of-order execution, etc., getting such timings is nearly impossible. Also, in a life prior to AMDAHL, I worked for a S/3 competitor whose machines were ASCII based. We used relative addressing instructions. Once I got use to it, I often wondered why this was not implemented by IBM in the S/3x0 architecture. Regards, Steve Thompson ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
