Agreed: Should have read "socket A" semprons, since these are the most common currently although rapidly disappearing... >*1* type of Sempron is an Athlon XP processor, the Socket-462 >versions. With the Socket-754, it is an Athlon 64, although >most have their 64-bit functions disabled. Only the lastest, >specifically branded Sempron 64 have the same, full >compatibility as their more expensive brothers. Bryan J. Smith wrote: >Tom <admin at homemachine.net> wrote: > > >>Hi all, >>Is it ok to use the i686 kernel in an AMD Sempron or should >>I be using another? >> >> > >To begin, know there are *3* different types of Semprons ... > >1. All Socket-462 Semprons are 32-bit only >They are Throughbred/Barton core (last rev Athlon XP) > >2. Most Socket-754 Semprons are 32-bit only >They are typically Newcastle core (mid-rev Athlon 64) with >the 52-bit addressing (PAE52) and other protions disabled > >3. New Socket-754 Sempron 64s are PAE52, 64-bit reg, etc... >Largely as an answer to Intel releasing the P4-Celeron EM64T, >AMD has stopped disabling the functionality of the cores. A >few are even newer Winchester (Rev. D), although I haven't >seen a Venice (Rev. E -- SSE support) Sempron 64 > >Now regarding the kernel, know these facts ... > >A. Athlon optimizations -- especially in GCC 3.3 (3.4 seems >to be much better) -- are not always stable (at least with >-O3). So even if you load an Athlon optimized kernel, GCC is >typically using -O2. On kernel 2.4, you'll see maybe a 5-15% >performance improvement. > >B. Linux Kernel 2.6 now adds [32-bit] Athlon optimizations >as a _dynamic_, modular support in the _stock_ i686 kernel. >There is little benefit to building a separate Athlon kernel, >as I've tried, and seen _no_ noticable improvement. > >C. If you load a x86-64 kernel, most of those _are_ already >optimized for Athlon architecture because they are the most >common. The 32-bit and 64-bit Athlons use the same core >scheduler design (with only a tiny variance), so just going >Linux/x86-64 now defaults to Athlon-optmizations. > >Personal Note: I found that rebuilding kernel 2.6 without >HIGHMEM support (960MiB memory max) increases performance >well over 15%, and the greatest increase possible with any >kernel change. > > >Ignacio Vazquez-Abrams <ivazquez at ivazquez.net> wrote: > > >>The i686 kernel is fine. If you're looking for (small) >>speedups then you're better off rebuilding the glibc >>and openssl packages for athlon. >> >> > >Agreed. But be careful in throwing the -O3 switch. Stick >with --target=athlon, which the SPEC file should just use -O2 >by default. > > >Peter Farrow <peter at farrows.org> wrote: > > >>The Sempron is essentislly an Athlon XP processor, so I >>would use the Athlon kernel... >> >> > >*1* type of Sempron is an Athlon XP processor, the Socket-462 >versions. With the Socket-754, it is an Athlon 64, although >most have their 64-bit functions disabled. Only the lastest, >specifically branded Sempron 64 have the same, full >compatibility as their more expensive brothers. > > >Peter Farrow <peter at farrows.org> wrote: > > >>Note: In some rare cases I have seen Athlon systems hang >>at boot on i686 kernels, and vice versa, this seems to be >>system board chipset related.....so don't take out any >>kernels you intend to replace until you have seen the >>system boot reliably.. >> >> > >There were various errata with Athlons (not always AMD's >fault), including: >- Intel changing the i686 ISA slightly with the P3/P4 (breaks >even i486 compatibility, sometimes even i586/Pentium). >- Intel 4M paging mode (AGP coherency issue in the Athlon's >on-board AGPgart, long, long story -- 4K paging is no lower >performance on Athlon, so 4M should never be used) >- ViA ATA and other southbridge peripherals failing >- SiS I2C compatibility issues >- Many others > >Nothing unheard of and not without some equivalents in the >Intel world (such as ICH ATA issues), but still notable. > > >Karanbir Singh <mail-lists at karan.org> wrote: > > >>There is no Athlon kernel in CentOS4.... as Ignacio has >>pointed out, should you need that small performance boost, >>then build yourself. >> >> > >If you have less than 1GiB RAM, then rebuilding without >HIGHMEM support would yield a much greater boost. > >I had this discussion over on the Fedora-Devel list back >after Fedora Core 2 came out and I complained about not >having a separate Athlon kernel. In the 2.6 kernel, the i686 >kernel dynamically loads support for Athlon optimizations, >instead of having a separate kernel. > >Sure enough, the boost I saw was because I removed HIGHMEM >support. I rebuilt the exact same configs with i686 and >Athlon and saw no difference whatsoever on kernel 2.6. >Apparently Linus concept of making optimizations more dynamic >for various i686 ISA compatible processors (C3/Geode, Athlon, >even P4, etc...) really works. > > >Tom <admin at homemachine.net> wrote: > > >>Ah yes, that's why I asked as I couldn't find an Athlon >>kernel for 4.1 :) Will there be one? >> >> > >Red Hat will not be adding one in the FC2+/RHEL4+ series >because of their view on the kernel 2.6 modular design. >Given my own testing (despite my initial reluctance), they >are indeed correct. > >I'll try to find the post in the LKML (Linux Kernel Mailing >List) that covers how the dynamic support works in the i686 >kernel. I know from what I've read before, there was just so >much overlap combined with so many i686 variants, there was a >real wish to see a more "core" i686 base with loadable >optimizations for Geode/C3, Athlon, P4, etc... > > > > >