Code location sensitivity of timings

[nidud]

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[dedndave]

i suppose you could use VirtualProtect to allow writes in the .CODE section
then, copy the code under test into a common code address space before executing it

http://msdn.microsoft.com/en-us/library/windows/desktop/aa366898%28v=vs.85%29.aspx

to help speed testing up a little....
you could use different counter_begin loop count values for the short and long tests
i try to select a loop count that yields about 0.5 seconds per pass

[dedndave]

prescott w/htt - xp sp3
unaligned

Code Select Expand

Intel(R) Pentium(R) 4 CPU 3.00GHz (SSE3)
------------------------------------------------------
4925905 cycles - 2048..4096  (164) A memcpy SSE 16
4933332 cycles - 2048..4096  (164) A memcpy SSE 16
4953203 cycles - 2048..4096  (164) A memcpy SSE 16
4963909 cycles - 2048..4096  (164) A memcpy SSE 16
4923198 cycles - 2048..4096  (164) A memcpy SSE 16
4941277 cycles - 2048..4096  (164) A memcpy SSE 16

11502669        cycles - 2048..4096  (164) U memcpy SSE 16
11487135        cycles - 2048..4096  (164) U memcpy SSE 16
11564951        cycles - 2048..4096  (164) U memcpy SSE 16
11570118        cycles - 2048..4096  (164) U memcpy SSE 16
11497558        cycles - 2048..4096  (164) U memcpy SSE 16
11526087        cycles - 2048..4096  (164) U memcpy SSE 16

aligned

Code Select Expand

Intel(R) Pentium(R) 4 CPU 3.00GHz (SSE3)
------------------------------------------------------
4935114 cycles - 2048..4096  (164) A memcpy SSE 16
4934727 cycles - 2048..4096  (164) A memcpy SSE 16
4942523 cycles - 2048..4096  (164) A memcpy SSE 16
4924574 cycles - 2048..4096  (164) A memcpy SSE 16
4924658 cycles - 2048..4096  (164) A memcpy SSE 16
4937763 cycles - 2048..4096  (164) A memcpy SSE 16

11490869        cycles - 2048..4096  (164) U memcpy SSE 16
11481780        cycles - 2048..4096  (164) U memcpy SSE 16
11616596        cycles - 2048..4096  (164) U memcpy SSE 16
11530420        cycles - 2048..4096  (164) U memcpy SSE 16
11488318        cycles - 2048..4096  (164) U memcpy SSE 16
11504392        cycles - 2048..4096  (164) U memcpy SSE 16

[nidud]

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[dedndave]

hmmm - that seems wrong
i thought you had to be in a code section to assemble instructions
guess i've never tried it - lol

but - there is nothing to prevent you from putting a proc in the code section and copying it to another address
so long as you allow writes into the affected pages with VirtualProtect and PAGE_EXECUTE_READWRITE

http://msdn.microsoft.com/en-us/library/windows/desktop/aa366786%28v=vs.85%29.aspx

[nidud]

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[dedndave]

i hadn't thought about that
but - most win32 CALL's are near relative
so, you'd have to translate the target addresses

but - for testing algorithm code that doesn't make any calls, like loops, etc,
the branch addresses are relative, but the target moves with the code   :P

if you wanted to use calls or invokes in movable code,
you could store the branch address and use CALL DWORD PTR lpfnFunction
or MOV EAX,Function and CALL EAX

[nidud]

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[nidud]

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[nidud]

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[dedndave]

hard to test individual instructions
so much relies on the surrounding code

[nidud]

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[nidud]

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[nidud]

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[dedndave]

those tests run way too fast to get reliable readings

for best results:
1) bind to a single core
2) wait about 750 mS before performing any tests - this allows the system to settle
3) adjust individual loop counts so that each test pass takes about 0.5 seconds

Code Select Expand

Intel(R) Pentium(R) 4 CPU 3.00GHz (SSE3)
STRCHR-------------------------------------------
170724  cycles - (  0) 0: crt_strchr
172046  cycles - ( 29) 1: x
70540   cycles - (119) 2: 'c'
62934   cycles - (107) 3: 'cccc'

170343  cycles - (  0) 0: crt_strchr
167063  cycles - ( 29) 1: x
89640   cycles - (119) 2: 'c'
82154   cycles - (107) 3: 'cccc'

240068  cycles - (  0) 0: crt_strchr
87783   cycles - ( 29) 1: x
25549   cycles - (119) 2: 'c'
23995   cycles - (107) 3: 'cccc'
--- ok ---

H:\nidudString\string\strchr => strchr

Intel(R) Pentium(R) 4 CPU 3.00GHz (SSE3)
STRCHR-------------------------------------------
209073  cycles - (  0) 0: crt_strchr
221060  cycles - ( 29) 1: x
80107   cycles - (119) 2: 'c'
83854   cycles - (107) 3: 'cccc'

198648  cycles - (  0) 0: crt_strchr
211263  cycles - ( 29) 1: x
106992  cycles - (119) 2: 'c'
96168   cycles - (107) 3: 'cccc'

253182  cycles - (  0) 0: crt_strchr
84552   cycles - ( 29) 1: x
26531   cycles - (119) 2: 'c'
36056   cycles - (107) 3: 'cccc'

they're all over the place   :P