Re: [boost] [xpressive] Performance Tuning?

Subject: Re: [boost] [xpressive] Performance Tuning?
From: Edward Grace (ej.grace_at_[hidden])
Date: 2009-07-31 13:29:55

>>> I ran the Visual Studio build again, still got about the same as  
>>> I got
>>> in my last email, so yea, Visual Studio is a lot better on templates
>>> then GCC is.  I wonder why GCC performs so much worse...
>>
>> Indeed - an open issue.  Perhaps I will play with some other  
>> options (march
>> etc.) to see if there's something I've overlooked.  Well, I have  
>> to say I'm
>> gaining more respect for the MS compiler - I last used it a very  
>> long time
>> ago, back then it was awful!
>>
>
> *scratches head*
>
> I must be missing something very obvious, but I do not see how your
> and OvermindDL benchmarks can support this conclusion: as far as I can
> tell, you two never compared the two compilers directly, what you are
> seeing is that on GCC the speed up of qi_parse over atoi/strtol is
> less than that of MSVC, but this tells nothing about the absolute
> performance of the two compilers on this test (i.e. you never showed
> any absolute times).

As you can probably guess I don't really like absolute times. It is  
simple enough to try and do a cross comparison in a similar manner to  
the way relative values are currently calculated - it will just need  
a bit of tweaking, I'll give that some thought.

> For what we know the gcc atoi might just be faster than msvc one. And
> in fact a quick google search brings these two pages:
>
>   http://tinyurl.com/mqa5yl [msvc8 atoi performance is 58% of that  
> of msvc6]
>   http://tinyurl.com/mzyw66 [thread containing a comparison of atoi
> functions of different languages and compilers, in particular it seems
> that MSVC atoi is really 2 times slower than gcc atoi]
>
> A slow atoi on MSVC would explain such a difference in the tests,
> assuming that the ability of both compilers to optimize qi_parse is
> about the same.

Ah, good point - mea culpa!  This is where my (diminishing) ignorance  
of computers gets highlighted - I was under the impression that the  
standard library calls would be calling the same underlying things  
for both compilers - clearly I'm mistaken.

Thanks for the comment.  My code was not originally intended for  
benchmarking compilers / platforms - it's just getting that way!

-ed
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"No more boom and bust." -- Dr. J. G. Brown, 1997