Accurate multi-threaded 64-bit counters on a 32-bit machine

while checking for updates on azillionmonkeys today, i have had an idea reading the code there.
it may achieve 2 benefits:
1) save some power while spinning
2) smooth aggressivity of the thread, allowing other threads to hit successfully

Code:

 mov esi,ADDER_VALUE and 0xffffffff
 mov edi,ADDER_VALUE shr 32
                        
.loop:
  pause 
  times 4 nop
  mov eax, dword [counter]   ; [[1]]
  mov edx, dword [counter+4] ; [[2]]
  mov ebx, eax
  mov ecx, edx
  add ebx, esi
  adc ecx, edi
  lock cmpxchg8b  qword [counter]        ; [[3]]
  jnz .loop

  dec [count]
  jnz .loop
  ret

the pause works as an hint for newer processors "entering a locking loop".
it translates to a "nop" on older processors. the 4 nop there have been calculated on latency/rec.througput of the following instructions
their goal should be to desynchronize the loop, using half the latency of itself, resulting so as "yelding" other threads
the access to the resource. here following tests on Yorkfield (Quad 45nm)

revolution_atom64.exe

Code:

unsafe  Count:156602052344132608 Time:125
unsafe2 Count:200000000000000000 Time:1451  <---
oldsafe Count:200000000000000000 Time:2074
safe    Count:200000000000000000 Time:1592

unsafe  Count:140552233700888576 Time:110
unsafe2 Count:200000000000000000 Time:1482   <---
oldsafe Count:200000000000000000 Time:1918
safe    Count:200000000000000000 Time:1358

unsafe  Count:140235594251510784 Time:109
unsafe2 Count:200000000000000000 Time:1545   <---
oldsafe Count:200000000000000000 Time:2012
safe    Count:200000000000000000 Time:1295

stabler results. then running 8 threads all-together,all of them using the proc above, accessing 4 counters,

atom64.exe

Code:

Counter:2000000000001000 Time:1294
Counter:2000000000001000 Time:1294
Counter:2000000000001000 Time:1294
Counter:2000000000001000 Time:1294

Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279

Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279
Counter:2000000000001000 Time:1279

very stable, and fast. to confirm this i managed to run the same tests on
my older P4 650 Prescott 90nm, single core

revolution_atom64.exe

Code:

unsafe  Count:111203394649338880 Time:406
unsafe2 Count:200000000000000000 Time:1454 <---
oldsafe Count:200000000000000000 Time:2265
safe    Count:200000000000000000 Time:1578

unsafe  Count:109429369441373184 Time:422
unsafe2 Count:200000000000000000 Time:1469  <---
oldsafe Count:200000000000000000 Time:2265
safe    Count:200000000000000000 Time:1578

unsafe  Count:113975042205012992 Time:407
unsafe2 Count:200000000000000000 Time:1578  <---
oldsafe Count:200000000000000000 Time:2250
safe    Count:200000000000000000 Time:1593

unsafe  Count:111315688249406464 Time:422
unsafe2 Count:200000000000000000 Time:1484  <---
oldsafe Count:200000000000000000 Time:2250
safe    Count:200000000000000000 Time:1594

and again 8 threads, accessing 4 counters

atom64.exe

Code:

Counter:2000000000001000 Time:593
Counter:2000000000001000 Time:593
Counter:2000000000001000 Time:593
Counter:2000000000001000 Time:593

Counter:2000000000001000 Time:312
Counter:2000000000001000 Time:312
Counter:2000000000001000 Time:312
Counter:2000000000001000 Time:312

Counter:2000000000001000 Time:704
Counter:2000000000001000 Time:704
Counter:2000000000001000 Time:704
Counter:2000000000001000 Time:704

Counter:2000000000001000 Time:453
Counter:2000000000001000 Time:453
Counter:2000000000001000 Time:453
Counter:2000000000001000 Time:453

and this is pretty satisfying, imo.
Cheers,
Very Happy