Re: (Almost) Rock-n-Roll - "The Bunny Hop" (1953)

On 10/01/2025 07:58, 186282@ud0s4.net wrote:

On 1/10/25 2:11 AM, The Natural Philosopher wrote:

On 10/01/2025 00:33, 186282@ud0s4.net wrote:

I've been trying to find out
   if with modern 'flat address space' CPUs there's
   any speed advantage in setting functions and
   data blocks at specific addresses - what in the
   old days would have been 'page boundaries' or
   such. In short does an i7 or ARM and/or popular
   mem-management chips have less work to do setting
   up reading/writing at some memory addresses ?
   Maybe a critical app could run ten percent faster
   if, even 'wasting' memory, you put some stuff in
   kind of exact places. Older chips with banked
   memory and even mag HDDs, the answer was Yes.

>
Mm.
>
I don't think so. About the only thing that is proximity sensitive is cacheing. That is you want to try and ensure that you are operating out of cache, but the algorithms for what part of the instructions are cached and what are not is beyond my ability to identify, let alone code in...

    I did a lot of searching but never found a
   good answer. IF you can do stuff entirely
   within CPU cache then it WILL be faster.
   Alas not MUCH stuff will be adaptable to
   that strategy - esp with today's bloatware.
 

RK is probably the best person to understand that, but in fact a modern compiler will optimise for a specific processor architecture normally. It is quite instructive to see how 'real world' programs speed up on a chipset that simply has more cache.

   We MAY be talking maker/sub-brand specifics ...
   intel i3/i5/i7/i9 may all be different. Different
   gens different yet. ARMs too.
 

Of course. And indeed many architectures are optimised for e.g. C programs.
Imagine if you chipset detects a 'ca;; subroutine' code nugget and then proceeds to cache the new stack pointer's stack before doing anything. All your 'local' variables are now in cache.

   Seems that CPUs and MMUs can do certain register
   ops faster/easier than others - fewer calx and
   switching settings. Therein my quest. If you want
   some code to run AS FAST AS POSSIBLE it's worth
   thinking about.

And compilers do.
And chipsets do,.
So we don't have to. I used to do *86 assembler, but what todays C compilers spit out is better than any hand crafted assembler is.
My mathematical friend only uses assembler to access some weird features of a specific intel architecture to do with vector arithmetic. He writes C library functions in assembler to access them.
Because the compilers don't acknowledge their existence - yet.
--
"I guess a rattlesnake ain't risponsible fer bein' a rattlesnake, but ah puts mah heel on um jess the same if'n I catches him around mah chillun".