On Mon, 17 Oct 2005, [EMAIL PROTECTED] stated: > On Sunday 16 October 2005 19:31, Nix wrote: >> These are synonyms for the same thing, as is -march=opteron and >> -march=athlon-fx. > >> -march=x86-64 is similar but disables use of 3DNow intrinsics (not that >> those are used much yet unless you use vector stuff a lot: I guess when >> OpenMP and autovectorization start to turn up in GCC trunks, we'll see >> more use from them). > >> (As far as I can tell PROCESSOR_K8 and PROCESSOR_ATHLON are identical in >> GCC except for bitness, a few predefined macros, and scheduling.
I was wrong: the K8 has faster vector ops, and GCC can use those. > I don't know, but I exactly expected scheduling to be changed. I was wrong; except for the vector-instruction stuff, Athlon scheduling is used. I shouldn't try to read GCC source while thick with cold. Instruction costs differ between K8 and Athlon, though (unlike Intel AMD still provide instruction timings, so they're accurate, too). That might well affect scheduling. > You may > correct > me (you know more about GCC), but I expect scheduling to make some > difference. Btw, I still haven't done the tricks to make UML use host cpu > features - it's still compiled with default GCC settings for this. Not a killer: those of us who really care will have made GCC default anyway by specifying --with-cpu or a target-specific triplet to GCC configure. > Actually, for the host kernel (which uses arch=k8, see arch/i386/Makefile)) > SSEx makes no difference (the kernel can't allow GCC to use FP on its own, as > you probably know - the kernel must explicitly enable FP state saving, and > even then there are strict rules on FP usage, for instance you must be > atomic). Well, actually, if you don't specify -ffreestanding, GCC can implement large block moves by going via SSE or MMX regs. (How common this is I'm not sure. Probably not very, especially for MMX.) -- `"Gun-wielding recluse gunned down by local police" isn't the epitaph I want. I am hoping for "Witnesses reported the sound up to two hundred kilometers away" or "Last body part finally located".' --- James Nicoll ------------------------------------------------------- This SF.Net email is sponsored by: Power Architecture Resource Center: Free content, downloads, discussions, and more. http://solutions.newsforge.com/ibmarch.tmpl _______________________________________________ User-mode-linux-user mailing list User-mode-linux-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
