On Sat, 11 Nov 2017 08:48:02 -0700, "James Van Buskirk"
wrote:
>Looking at your code more carefully, it seems to consist of three
>blocks like:
>
>mov rax, rdi
>and rax, [mem]
>mul [mem]
>sub rdi, rdx
>
These parts of the code
mul qword ptr [c_1] # 3 2 2 1 3 2
sub rdi,rdx # 1 1 x x x 1 0-33
mov rax,rdi # 1 1 x x x 1 0.33
and rax,qword ptr [m_2] # 1 1 x x x 1 1
I figured fit that rule: ?
#####
Instruction decoding
The decoders can handle four instructions per clock cycle, or five in
the case of macro-op fusion. Only the first one of the four decoders
can handle instructions that generate more than one ľop. The minimum
output of the decoders is therefore 2 uops per clock cycle in
the case that all instructions generate 2 uops each so that only the
first decoder can be used. Instructions may be ordered according to
the 4-1-1-1 pattern for optimal decoder throughput.
#####
I tried to verify this by inserting RET at the places with these
lines:
# ? cycles
for instance:
RET
# 6 cycles
gives an output of ~6,000,000.
>There is a fourth block in there, but since it doesn't write rdi,
< ...
>to devise some more tests to check these possibilities out.
>Also, a million iterations is quite a lot and could catch an
>interrupt quite frequently. Normally I would do a lot less
I assemble and link it in geany and when I click the execute button
directly in the GUI the output varies very often, so I think it
catches many, but in an X-terminal there are very few differences in
the output. It mostly reads ~12,000,000 with an occasional higher one.
>iterations -- 100 would be plenty -- and store the results
>in an array. After doing a small number of timings, 10 or
>less, print out the array. Make some sort of judgment
>about the noise you see in your data. And print out the
>raw results of your program: not everyone has a Nehalem
>running 64-bit linux for direct verification.
>
I should have told that I actually run this in a guest "Linux debian
4.9.0-3-amd64" in virtualbox on a Windows 10 host, and the cpu has
3.4GHz, but AFAICT the guest does run in real time (not sure though).
--
aen
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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