Hi Arjan,

Most likely we'll be optimising the entire distro for P4 while keeping compatibility with i386 or i486. (Code optimized for P4 runs just as fast as code for pII/pIII on those).

This issue was discussed in the thread "Making NPTL the default for FC3, vanilla i386 support". Both i386s and i486s are already no longer supported since FC 1. Try running rpm on either of these CPUs and see it fail. See https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=103078 .

So if there is the intention of making the move to i486 as the minimum arch we could just as well make the jump to i586.

Leonard.

Hi Alan,

It depends which 486 variant, and its only rpm thata affected.

Plus db4 (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=91933). But indeed nothing else that I am aware of. Maybe these packages should be tagged i686 for this reason. Calling them i386 gives the wrong impression of compatibility. This way i386 users can easily tell these are packages that need to be patched.

More relevantly, dropping 486 compatibility buys you nothing. The pentium added no useful "essential" instruction that makes a big difference while the 486 added several features

Ok. That seems to be a good reason not to bump to i586. Still leaves the question if we need to bump to i486.

Leonard.

On Monday 31 May 2004 09:39, Jakub Jelinek wrote:

On Mon, May 31, 2004 at 09:22:04AM +0200, dragoran wrote:

...

Why not add a glibc and kernel which are optimized for pentium 4 in FC3 ? This would increase the perfomance on newer PC but also works on older ones by still including the i686 and i586 versions.

Starting with FC3, .i386.rpm and .i686.rpm packages will be compiled with -march{3,6}86 -mtune=pentium4, so although they will run on i386 (resp. i686), they will be optimized for P4 (Athlons and newer AMD chips run P4 optimized code without noticeable performance hit).

Hi !

Is there difference betwwen -mtune=pentium4 and -mtune=athlon ? Pentium4 sounds intel-ish centric but what about AMD ?.

cristian

On Mon, 2004-05-31 at 10:10, Jakub Jelinek wrote:

On Mon, May 31, 2004 at 04:50:59PM -0400, Balint Cristian wrote:

...

...

Starting with FC3, .i386.rpm and .i686.rpm packages will be compiled with -march{3,6}86 -mtune=pentium4, so although they will run on i386 (resp. i686), they will be optimized for P4 (Athlons and newer AMD chips run P4 optimized code without noticeable performance hit).

Is there difference betwwen -mtune=pentium4 and -mtune=athlon ? Pentium4 sounds intel-ish centric but what about AMD ?.

Yes, there is. The thing is, Intel chips are far more sensitive to instruction scheduling than AMD chips. So, if you run code tuned for AMD on P4, the performance hit is big, if you run P4 optimized code on AMD, the performance hit compared to running AMD tuned code on AMD is really small.

Jakub

I think it is only fair that someone quantify the performance hit that K7 and 32bit K8 users can expect versus the improvement that P4 users will see before this is implemented. Is this change in anticipation of the Prescott with its even deeper instruction pipeline? It is my understanding that 32bit-only K8s are shipping already...since they are being pitch at all areas outside the NA and Europe, they ought to be considered also before a final decision is made here.

If I am reading this right, not only the kernel and glibc will be affected...it was stated that the *entire* distro will be optimized for the P4. People seem to have accepted the idea that K7 optimized kernels aren't worth the effort...but if we are now talking a performance hit across the board on all apps not run on Intel hardware, there may be some unhappy campers. With the 7% performance hit once mentioned here due to SELinux, just what is a "really small" performance hit? I'm not sure I will happily accept another 5% loss because I don't run P4s. Rolling my own kernel is one thing...having to rebuild everything on all my boxes isn't...I might as well go back to LFS or Gentoo if this is the case.

It would be interesting to know the ratio of P4 to K7 Fedora users to determine if this optimization is a great idea since this thread implies that it would require more resources that RH is willing to apply to also give us K7 optimized RPMs...or is the logic because corporate America continues to be sucked in by Intel's marketing? While I have no doubt that Intel dominates the RHEL market, I do wonder if the same can be said for the Fedora community.

KAS

On Mon, May 31, 2004 at 06:15:07PM +0200, Arjan van de Ven wrote:

hurt p4's while ADD/SUB by one are fast), AMD cpus seem to not care really which form is chosen, it seens AMD optimizes in the cpu beyond this level. You'll be *really* hard pressed to find (artificial) examples where this would slow down AMD cpus even 0.1%....

Likewise my own testing has always found that the Athlon really doesn't care much how you order instructions. If you think about it AMD have spent years dealing with everyone optimising for random intel processor of the year and adapted appropriately. Except on things like 3dnow and prefetch stuff the AMD really doesn't seem to care.