Re: [Patch, Darwin, I386] enable mtune=core2 on darwin and make it the default.

[IainS <developer at sandoe-acoustics dot co dot uk>]

On 13 Aug 2010, at 20:25, Jack Howarth wrote:

> On Fri, Aug 13, 2010 at 06:36:12PM +0100, IainS wrote:
> > Hi HJ,
> >
> > On 13 Aug 2010, at 18:22, H.J. Lu wrote:
> >
> > > On Fri, Aug 13, 2010 at 9:39 AM, IainS
> > > <developer@sandoe-acoustics.co.uk> wrote:
> > > > In order to do that it was necessary to get -mtune=core2 to work ..
> > > > ... this had a couple of residual cases where the use of movq is
> > > > incompatible with the darwin  assembler.
> > >
> > > Do you know -mtune=core generates slower code than -mtune=generic?
> >
> > I have not benchmarked - unfortunately, we volunteers do not have  
> > access
> > to SPEC &c.


>     I can repeat the benchmarks this weekend but the last time I  
> looked
> at the performance of the Polyhedron 2005 benchmarks on x86_64-apple- 
> darwin10,
> I found -mtune=core2 was slower than -mtune=generic.

Do you have any reasonable body of c/c++ benchmarks?
I have the Polyhedron fortran ones.

Odd that the vendor would choose that default if it's genuinely less  
performance...
I guess I could look and see if there are changed tuning params...

... anyway I'm not going to nail colors to the mast over this one -  
it's easily changed.

... remember the old BYTE article "Lies, Damned Lies & Benchmarks" ?

cheers,

Iain