Sent from my new iPad > On 29 Apr 2016, at 18:10, Peter Relson <[email protected]> wrote: > > Since the origin for the starting post apparently lay in branching around > the eyecatcher (which really is not necessarily at all the same as a > branch in a 2 instruction loop), I was surprised that none of the posts > that I glanced at mentioned Instruction-cache misses. > > Just because you think something is high frequency does not mean that the > operating system or the machine agrees with you. If the module's first > instruction is not in I-cache, then whether that first instruction is a > branch or anything else, it will show up as a lot hotter than a somewhat > similar instruction that is in the I-cache.
That's an interesting point: does this mean that every instruction at the start of an 256 byte boundary will probably appear hotter because it sits at the start of a cache line and profilers will attribute the time it takes to load the line into cache to this instruction? The other instructions in the cached line quietly benefit from this behavior. You could probably validate this by inserting NOPS in the code. The hotspots should shift by the length of the NOP. And the entry point of a module might be more likely to sit on a 256 byte boundary if it is also at the very start of the code of that module... Very interesting. Fred! ---------------------------------------------------------------- ATTENTION: The information in this e-mail is confidential and only meant for the intended recipient. If you are not the intended recipient , don't use or disclose it in anyway. Please let the sender know and delete the message immediately. ------------------------------------------------------------------------------------------------------ ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
