[Python-Dev] Summary: rejection of 'dynamic attribute' syntax

[Thomas Heller]

Steve Holden schrieb:
> Ben North wrote:
> [...]
>> Guido van Rossum wrote:
>>> I missed discussion of the source of the 1%. Does it slow down pystone
>>> or other benchmarks by 1%? That would be really odd, since I can't
>>> imagine that the code path changes in any way for code that doesn't
>>> use the feature. Is it that the ceval main loop slows down by having
>>> two more cases?
>> 
>> That seems to be it, yes.  I tested this by leaving the grammar,
>> compilation, and AST changes in, and conditionally compiling just the
>> three extra cases in the ceval main loop.  Measurements were noisy
>> though, as Josiah Carlson has also experienced:
>> 
>>> I've found variations of up to 3% in benchark times that seemed to be
>>> based on whether I was drinking juice or eating a scone while working.
>> 
>> I'm afraid I can't remember what I was eating or drinking at the time I
>> did my tests.
>> 
> A further data point is that modern machines seem to give timing 
> variabilities due to CPU temperature variations even if you always eat 
> exactly the same thing.
> 
> One of the interesting facts to emerge from the Need for Speed sprint 
> last year is that architectural complexities at many levels make it 
> extremely difficult nowadays to build a repeatable benchmark of any kind.

My personal experience using a dual core machine (on WinXP) is that timing
results become much more reproducible.

Thomas