Re: GCC 3.3, GCC 3.4

[Benjamin Kosnik <bkoz at redhat dot com>]

>> we're not really getting any faster.
>
>Yes, it really is faster.  It really is better.  Consider for example 
>that we had the value be 2KB, and 1% increase, and someone said bumping 
>it up to 30% and 8MB is wrong and just papers over the real problem.  
>We'd laugh at them, just the same way I laugh at you now.

You know, I agree with you. I could not figure out why Neil was saying
this, when I posted real timing numbers, based on increased numbers, and
others backed me up. 

It seems as if the defaults were set arbitrarily: testing with various
numbers tells me that bumping up to 16MB gets the maximum bang for the
minimum setting.

Holding on to these poorly picked initial numbers, in the face of data
that suggests a better set of number, seems to be incredibly foolish.

Neil, did you miss out on the Monday thread on the garbage collector?

>We have two ways of fixing the problem, one trivial, and one hard, you 
>suggest not fixing it the easy way, because we'd rather not fix it, 
>than fix it the easy way?  [blink]

Or not fix it. Which seems to be what is happening.

>The changes are not mutually exclusive.  Both changes make gcc better.  
>Each change by itself makes gcc better.

Right.

>Also, some of the slowdown as laid at the feet of a much larger 
>libstdc++, not that that is bad, it just is.  Now with PCH, maybe we 
>want to have a header called <all> that includes all the normal C++ 
>headers and precompile it, and switch all the normal C++ headers to 
>#include <all>.
>Hello world then sees a nice speed improvement.

Some of the slowdown between 2.95 and 3.0 can be laid at the feet of
libstdc++. The slowdown between  3.0 and 3.2, 3.2 and 3.3, and 3.4
cannot.

I sent Geoff K a way to make the standard C++ pch. I, and others,
continue to work with him to make C++ + pch play nice. If you're
interested, search gcc and other categories in GNATS for [pch]. 

You can count on libstdc++ changes to use PCH as soon as it becomes possible.
 

best,
benjamin