> -----Original Message----- > From: IBM Mainframe Assembler List [mailto:ASSEMBLER- > [email protected]] On Behalf Of John Gilmore > Sent: Tuesday, April 16, 2013 12:29 PM > To: [email protected] > Subject: Re: TRTE and new instructions > > Peter Farley's points are interesting ones. My numbers tell a very > different tale, and I suspect that these differences turn on when such > measurements are taken. > > The first appearances of new instructions, millicoded ones anyway, do > often exhibit 'bad' performance; but this performance sometimes, even > usually, improves rapidly. > > Working with millicoded instructions has taught me two important > lessons: Their performance is a moving target, and early measurements > of it are usually misleading. It often improves significantly in the > interval that would be required to replace them with alternative > sequences.
I don't get to work at this level often, but I am always interested. How can Millicode be faster than the equivalent using the hardware instructions? As I understand Millicode, that is really all it is (using the hardware instructions) plus any overhead in context switching to the Millicode "environment". For the MVC/MVCL option, I can imagine a macro which generates an MVC loop, or unroll the loop into a sequence of MVC, or generate the MVCL depending on several criteria. I currently don't have the knowledge to determine the criteria and I would expect the criteria to change over time. > > John Gilmore, Ashland, MA 01721 - USA
