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Re: Why not 03 ?

On Sun, Jun 01, 2014 at 12:37:18AM +0200, Tollef Fog Heen wrote:
> ]] Steve Langasek 

> > FWIW, the recent port of Ubuntu to ppc64el uses -O3 as the default, because
> > IBM has broad experience in resolving performance issues for their own
> > hardware and have found that -O3 gives an overall better experience for
> > their customers.  It will be difficult for Debian to gather the same kind of
> > information across all its architectures, but we shouldn't conclude, just
> > because it's difficult to know the right answer, that -O2 is definitely the
> > right answer.

> It sounds like we want to stop recommending any particular level in
> Policy and just let the architecture toolchain default to the
> recommended value for that architecture, and only override when there's
> a need.

It seems that I believed the policy language on this to be much stronger
than it actually is.  Looking at policy, I see:

     By default, when a package is being built, any binaries created should
     include debugging information, as well as being compiled with

It then presents CFLAGS = -O2 [...] as an example, but apparently this is
only an example.

Still, I think we're better off improving the policy language to explain
when we think -O3 should be used instead of -O2, and when it should not,
rather than having a free-for-all in the archive.  Even to make this change
on a per-architecture basis warrants more extensive profiling than porters
are probably prepared to do; I certainly don't want maintainers to override
it "when there's a need" without the project providing some guidance on what
constitutes sufficient "need".

Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

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