On Thu, Jun 30, 2016 at 9:53 AM, Jan Kratochvil <jan.kratochvil@xxxxxxxxxx> wrote: > On Thu, 30 Jun 2016 12:12:37 +0200, Dan Horák wrote: >> For ppc64 (the big endian POWER) the base is set by the toolchain >> default which is Power4/ppc970. When Power7 came we were asked what are >> the options to take the advantage of these CPUs, 3 generations newer >> than the base. The solution was the introduction of ppc64p7 subarch > > But now there is ppc64le for >=Power8. So <=Power7 can use ppc64 but newer >>=Power8 hardware does use ppc64le which is already Power8 optimized. > So isn't this problem (somehow temporarily) solved for now? POWER8 can run in either endian mode. So no, the problem is not solved. > Or are really the Power7 (and not yet Power8) machines the real problem? Realistically, it isn't about either specifically. Each iteration of POWER tends to require tuning specifically for that generation if you want to get the most performance out of your software. That tuning is incompatible with older generations of hardware (endian completely aside). So as Dan alludes to, this is fairly cumbersome. To make it widely useable, you default to the oldest generation you want to support. x86 theoretically has similar problems, but we tend to just not care as much about tuning at the distro level. The applications can tune however they'd like, but given that most datacenters are not homogeneous among x86 machines, it often means people cannot tune for one specific x86 generation because they have to run on a wider variety. Contrast that with POWER, where people using that tend to buy one or two very large systems to consolidate their workload on. They can and often do want the best performance they can eek out since they're consolidating, which means they often want the distro components tuned as well, particularly system libraries. Going forward, I'd seriously look at dropping anything older than POWER7 support. I know we all dearly love our Mac G5 machines (ppc970), but those are getting very very old at this point. POWER5 was a non-event for Fedora, POWER6 was a weird generation even for IBM. POWER7 and POWER8 are where most of the effort is, and that will only continue as next generation POWER chips come out. Given that Rackspace and others have actually started using the openPOWER stuff with POWER8, it probably makes sense to focus on where the users are headed and not where they were 10 years ago. josh -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://lists.fedoraproject.org/admin/lists/devel@xxxxxxxxxxxxxxxxxxxxxxx
