On 26/03/2018 13:30, Richard Damon wrote:
On 3/26/18 6:31 AM, bartc wrote:
The purpose was to establish how such int("...") conversions compare
in overheads with actual arithmetic with the resulting numbers.
Of course if this was done in C with a version that had builtin bignum
ints or an aggresive enough optimizer (or a Python that did a similar
level of optimizations) this function would just test the speed of
starting the program, as it actually does nothing and can be optimized
away.
Which is a nuisance. /You/ are trying to measure how long it takes to
perform a task, the compiler is demonstrating how long it takes to /not/
perform it! So it can be very unhelpful.
Hence my testing with CPython 3.6, rather than on something like PyPy
which can give results that are meaningless. Because, for example, real
code doesn't repeatedly execute the same pointless fragment millions of
times. But a real context is too complicated to set up.
Yes, something like this can beused to measure the base time to do
something, but the real question should be is that time significant
compared to the other things that the program is doing, Making a 200x
improvement on code that takes 1% of the execution time saves you
0.995%, not normally worth it unless your program is currently running
at 100.004% of the allowed (or acceptable) timing, if acceptable timing
can even be defined that precisely.
I'm usually concerned with optimisation in a more general sense than a
specific program.
Such a with a library function (where you don't know how it's going to
be used); or with a particular byte-code in an interpreter (you don't
know how often it will be encountered); or a generated code sequence in
a compiler.
But even 200x improvement on something that takes 1% of the time can be
worthwhile if it is just one of dozens of such improvements. Sometimes
these small, incremental changes in performance can add up.
And even if it was just 1%, the aggregate savings across one million
users of the program can be substantial, even if the individuals won't
appreciate it. 1% extra battery life might be a handy five minutes for
example.
--
bartc
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