On 2019-08-28 02:06, Paul Koning wrote:
On Aug 27, 2019, at 6:01 PM, Johnny Billquist <bqt%update.uu.se@localhost> wrote: ...- No need to save PSL or align stack. Keeping stack aligned is up to the compiler.I can't remember. Does CALL really align the stack? How is that then handled at return? Does it realign back to whatever it was previously?Yes, and yes. The alignment (2 bits) is part of the generated stack frame.
And, sorry for asking instead of trying to read the documentation, this alignment is not done in general for the stack? (Remember, I'm mostly working on PDP-11s these days...)
Anyway, I suspect the total change of the ABI is quite a lot of effort, with rather small effect. If we are to assume that every 10th instruction is a call, and we can improve the speed, in the end, by 50% of those calls, we're still only talking about a 5% speed increase, for quite a large effort. I feel that we're at the end of the line, unless the kernel is made simpler and more streamlined.
It has just become too heavyweight. And all older architectures suffer because of it, and I can't see any specialized optimizations like this making enough of a difference to be worth it.
Ok, so I'm pessimistic tonight... Oh well. :-)
Johnny
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|| on a psychedelic trip
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