Re: Compile performance of Linux kernels in mainline gcc

[Steven Bosscher <stevenb at suse dot de>]

On Saturday 30 October 2004 12:30, Giovanni Bajo wrote:
> Andi Kleen wrote:
> > Quick representative results:
> >
> > gcc 3.3-hammer:
> > 210.32user 31.62system 3:57.66elapsed
> >
> > 4.0 snapshot:
> > 262.71user 30.50system 4:48.46elapsed
> >
> > 4.0 is nearly a minute slower overall than 3.3. -O2 compile
> > performance is quite bad. Also the resulting kernel crashed early at
> > boot.
>
> While I do not necessarily agree, there have been some statements in the
> past about ignoring the compile time regression at -O2.

There have been statements in reaction to this bullshit too.
Optimizing compile time *does* matter.  Because *newsflash* most people
build with optimizations enabled.


> The idea is that
> 4.0 optimizes code much better (or: has many more optimizers)

Apparently, the latter.


> > The suse 3.3-hammer was compiled with profiledbootstrap, while
> > 4.0 only got an ordinary bootstrap (I can try it later with a
> > profiledbootstrap but I'm not sure I should expect much difference)
>
> Well, yes, try again. I remember impressive numbers about
> profiledbootstrap. I don't think it is going to be a 24% difference, which
> is the compile-time regression we see now.

profiledbootstrap used to make the compiler more than 10% faster.

Gr.
Steven