A few days ago, Frans said: > From a later discussion with some other people on IRC, it looks like > SSE support is probably the deciding factor. According to section > 2.2 in [1] and especially the note "Enabling SSE support" just above > section 2.3, models 0-5 for family 6 AMD processors may not have SSE > support and thus should continue to default to the 486 flavor.
Thanks for the research Frans and the follow-up on IRC. However, after thinking about this, I'm not sure I follow the logic - or at least I need some hand holding to get it. >From reading the kernel source, it appears that a 686-configured kernel will cause gcc to use -march=i686. The gcc manual[1] implies that this will not cause sse instructions to be generated - pentium3 or athlon optimization (or greater) is required before SSE is enabled. The kernel does have some assembly routines coded in assembly that make use of SSE (e.g. the xor code used for raid checksumming), but they dynamically check for sse support by using cpu_has_xmm(). I do see why we wouldn't want to run a k7 kernel on all family 6 cpus. Google quickly found a /proc/cpuinfo file that shows a family 6 with no sse flag. However, I don't follow why this means a 686 kernel would not be safe on a family 6 cpu. [1] http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/i386-and-x86_002d64-Options.html#i386-and-x86_002d64-Options [2] http://ubuntuforums.org/showpost.php?p=5119933&postcount=32 -- dann frazier -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]