Advanced Micro Devices Inc (AMD)

[HailMary]

Kevin McGrath talks Hammer.

Great presentation. Maybe too good. I think he gave away some helpful hints to competitors.

One of the things I liked hearing (there were many) was once in 64-bit long mode, the switch to the compatibility sub-mode was on the same order as a far call, or about 80 cycles. This is very good. As long as the app isn't making a zillion calls to the o/s, the 32 bit app should run well. The calls to the o/s may be made up for by the o/s code called will now be running in 64-bit mode with extra registers, so it may work out to be a net benefit for most 32-bit applications. Some o/s calls may be slower if the call is a short one as every 32-bit app to 64-bit o/s call has the mode switch and the wow64 windows layer to deal with.

Also interesting (although I already knew this) is seeing how the FP execution unit carries around the worst x86 baggage in the form of a few more pipe stages because of the old stack architecture. FP performance could probably be improved a bit if this could be dropped. I fear it will take many, many years before they start dropping legacy support just because they don't want to stop supporting an installed codebase. Until then, advantage IA-64. Fortunately it doesn't appear to matter much at the moment.