> Once upon a time IIRC there was a significant performance penalty for > non-aligned operands (loading a fullword from an address not evenly > divisible by four, etc.). Does that still exist for modern Z processors? > (Once upon a time it didn't work at all, but that's AFH, to use an acronym I > learned this week.) > > I have a string that looks like halfword, char, char, ..., halfword, char, > char, ... . It will be accessed millions of times per day in a system exit. > Would it be better to "pack" the halfwords immediately following the chars, > or halfword-align them with a slack byte where necessary? The access will be > read-only if that makes a difference.
Response from hardware designer: It depends on the system. z10 and before, if an operand crossed a DW there was a penalty. On z196 and later, it is only if an operand crosses a cache line. Of course things could change again in the future. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
