On Thu, 2005-06-09 at 10:03 -0400, Horst von Brand wrote: > Arjan van de Ven <arjanv@xxxxxxxxxx> wrote: > > > > Of course, on through -m64 was as expected. I'm just a bit surprised > > > that it didn't say mtune=k8 since it was definitely building on one ... > > > which begs the question ... is GCC (and hence the entire x86_64 > > > distribution) being built this way? What are the K8 performance > > > implications? I've seen a few things that indicate that Nocona cores > > > running K8 code look pretty bad in some areas compared to optimized > > > code...however, I find nothing to indicate how nocona optimized code > > > runs on the K8. > > > AMD cpus are very good at running just about anything you throw at it > > (think about it; with their marketshare... most code out there is > > optimized for intel cpus so their cpus are effectively required to deal > > well with such code). The reverse unfortunatly isn't the case. > > AFAIU, they are talking about /64 bit/ code here. There the situation is > almost exactly the other way around, isn't it? What Arjan is saying is this: AMD Opteron/Athlon64 CPUs do much, much better with -mtune=nocona than Intel EM64T CPUs do with -mtune=k8. It appears that the Opteron/Althon64 are more flexible in this regard. Therefore, since the hit for -mtune=nocona on Opteron is much smaller than -mtune=k8 on EM64T, the distro uses -mtune=nocona. The question, distilled: Would you like: (a) Small speed hit for Opteron users, OR (b) much larger speed hit for EM64T users? (a), ie -mtune=nocona everywhere, seems to be the fairest option here for everybody since we obviously cannot make 1 build of Fedora Core for Opteron and 1 comletely separate build of Fedora Core for EM64T. Dan -- fedora-devel-list mailing list fedora-devel-list@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/fedora-devel-list
