Re: [PATCH 3/3] Add basic PowerPC core tune config

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Tue, 2011-07-26 at 17:03 -0500, Kumar Gala wrote:
> On Jul 26, 2011, at 11:18 AM, Richard Purdie wrote:
> 
> > On Tue, 2011-07-26 at 10:22 -0500, Kumar Gala wrote:
> >> On Jul 26, 2011, at 8:59 AM, Richard Purdie wrote:
> >> 
> >>> On Tue, 2011-07-26 at 08:47 -0500, Kumar Gala wrote:
> >>>> On Jul 26, 2011, at 7:44 AM, Richard Purdie wrote:
> >>>> 
> >>>>> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
> >>>>> ---
> >>>>> meta/conf/machine/include/powerpc/arch-powerpc.inc |   45 +++++++++++++++++++-
> >>>>> meta/conf/machine/include/tune-ppc603e.inc         |   12 ++++-
> >>>>> meta/conf/machine/include/tune-ppce300c2.inc       |   12 ++++-
> >>>>> meta/conf/machine/include/tune-ppce500.inc         |   13 ++++--
> >>>>> meta/conf/machine/include/tune-ppce500mc.inc       |   12 ++++-
> >>>>> meta/conf/machine/include/tune-ppce500v2.inc       |   12 ++++-
> >>>>> 6 files changed, 88 insertions(+), 18 deletions(-)
> >>>> 
> >>>> One thing I'm wondering about as we do this is the ability to pass
> >>>> --with-cpu to gcc & [e]glibc configure to pickup proper optimized cfgs
> >>>> & libs for a given target.
> >>> 
> >>> As far as I can tell, gcc 4.x has no --with-cpu option. We pass the
> >>> correct march and mtune options to the compiler at runtime through
> >>> CFLAGS and friends.
> >> 
> >> Hmm, gcc still supports this:
> >> 
> >> http://gcc.gnu.org/install/configure.html
> >> 
> >> --with-cpu=cpu
> >> --with-cpu-32=cpu
> >> --with-cpu-64=cpu
> >> Specify which cpu variant the compiler should generate code for by default. cpu will be used as the default value of the -mcpu= switch. This option is only supported on some targets, including ARM, i386, M68k, PowerPC, and SPARC. The --with-cpu-32 and --with-cpu-64 options specify separate default CPUs for 32-bit and 64-bit modes; these options are only supported for i386, x86-64 and PowerPC. 
> >> 
> >> http://gcc.gnu.org/install/specific.html
> >> 
> >> powerpc-*-*
> >> You can specify a default version for the -mcpu=cpu_type switch by using the configure option --with-cpu-cpu_type.
> > 
> > I couldn't find that looking at the configure script :/.
> > 
> > Anyhow, according to that page, its to "Specify which cpu variant the
> > compiler should generate code for by default. cpu will be used as the
> > default value of the -mcpu= switch". Since we always specify -mcpu when
> > needed, I don't believe this is an issue for us as far as the build
> > system goes.
> > 
> > If you're talking about the gcc we build for the target, we should
> > really encode all the cpu/tune options in there, not just part of the
> > config so again, I don't think its appropriate to the way we use gcc.
> 
> What about tool chains produced as part of a ADT, wouldn't it be useful for such as case?
> 
> Seems like having ability to pass '--with-cpu' ends up being useful to set default for things like 32 vs 64-bit on multiple.

ADT passes an environment script with all the appropriate flags
contained within including tunings which --with-cpu doesn't help with so
I'm not sure its so useful there.

Cheers,

Richard