Robin Vowels wrote: >>But! In performance discussions on LinkeIn's "Mainframe Assembler >>Professionals" group, like this one: >> http://www.linkedin.com/groups/1462937/1462937-91082881 ... >>...I've learned that LOAD/STORE sequences (IC/STC, L/ST, LM/STM) are much >>faster than an equivalent length MVC. See comments in the above discussion >>such as: >>"CLC (like MVC) is very fast - but only after a start-up penalty. In the >>MVC case using two LG/STG is much faster than a 16 byte MVC..." >>and >>"There is a good reason why small MVCs run slower than LG/STG pairs. There >>is a bunch of overhead at the beginning of a MVC. Just one example: you >>have to check if the operands are on "good" boundaries. If not, you tiptoe >>your way to a good boundary. Then you can rip. Have to check for operand >>overlap conditions. There is a length check involved. During this time the >>LG/STG is far on its way. Some IBM machines (if I remember correctly) also >>had a bigger fetch/store path for MVC. Again, once it got going. I can >>assure you that a LG/STG pair is faster than a 16 byte MVC. Anyone writing >>a length-1 MVC instead of an IC/STC would be laughed out of their code >>review.
>Rubbish. What part of above paragraph you're referring to is rubbish? For my part, I'm also struggling to swallow that paragraph. I would rather read formal bookies confirming those statements. >KISS. >A move of length 1 is clear and unequivocal. >And it's only one line. Indeed, if you're thinking of MVI instead of MVC. Groete / Greetings Elardus Engelbrecht
