Messages in this thread | | | Date | Sat, 13 Sep 2003 17:11:49 +0100 | From | Dave Jones <> | Subject | Re: RFC: [2.6 patch] better i386 CPU selection |
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On Sat, Sep 13, 2003 at 02:51:03PM +0200, Adrian Bunk wrote:
> This patch makes the bzImage for my computer (same .config, same > compiler, same compiler options) a good 5 kB smaller.
For the invasiveness of the patch, 5KB really is a questionable gain..
> In 2.4 selecting e.g. M486 has the semantics to get a kernel that runs > on a 486 and above. > In 2.6 selecting M486 means that only the 486 is supported.
What are you basing this on ? This seems bogus to me. Last I checked, I could for eg, boot a 386 kernel on an Athlon.
> +config CPU_VIAC3_2 > bool "VIA C3-2 (Nehemiah)" > help > - Select this for a VIA C3 "Nehemiah". Selecting this enables usage > - of SSE and tells gcc to treat the CPU as a 686. > - Note, this kernel will not boot on older (pre model 9) C3s. > + Select this for a VIA C3 "Nehemiah" (model 9 and above).
You lost an important part of helptext.
> +config CPU_ONLY_K7 > + bool > + depends on CPU_K7 && !CPU_INTEL && !CPU_K6 && !CPU_K8 && !X86_ELAN && !CPU_CRUSOE && !CPU_WINCHIP && !CPU_CYRIXIII && !CPU_VIAC3_2 > + > +config CPU_ONLY_K8 > + bool > + depends on CPU_K8 && !CPU_INTEL && !CPU_K6 && !CPU_K7 && !X86_ELAN && !CPU_CRUSOE && !CPU_WINCHIP && !CPU_CYRIXIII && !CPU_VIAC3_2 > + > +config CPU_ONLY_WINCHIP > + bool > + depends on CPU_WINCHIP && !CPU_INTEL && !CPU_K6 && !CPU_K7 && !CPU_K8 && !X86_ELAN && !CPU_CRUSOE && !CPU_CYRIXIII && !CPU_VIAC3_2 > + default y
These are hurrendous. Each time we add support for a new CPU we have to update each and every one of these. This won't fly, someone *WILL* miss one. We've had this sort of thing happen before, and its an accident waiting to happen.
> + > +ifdef CONFIG_CPU_K8 > + ifdef CONFIG_CPU_PENTIUM4 > + cpuflags-y := $(call check_gcc,-march=pentium3,-march=i686) > + else > + cpuflags-y := $(call check_gcc,-march=k8,$(call check_gcc,-march=athlon,-march=i686 $(align)-functions=4)) > + endif > +endif > +
These horrible nesting things are also a real PITA, as theres >1 case that needs updating when something changes for a particular vendor/family. The cflags-$foo stuff in 2.6 was just starting to become readable, and you want to undo that?
> --- linux-2.6.0-test5-cpu/arch/i386/lib/mmx.c.old 2003-09-13 11:14:00.000000000 +0200 > +++ linux-2.6.0-test5-cpu/arch/i386/lib/mmx.c 2003-09-13 11:17:00.000000000 +0200 > @@ -121,7 +121,7 @@ > return p; > } > > -#ifdef CONFIG_MK7 > +#ifndef CONFIG_CPU_CYRIXIII > > /* > * The K7 has streaming cache bypass load/store. The Cyrix III, K6 and
wtf ?
> --- linux-2.6.0-test5-cpu/arch/i386/mm/init.c.old 2003-09-13 14:18:04.000000000 +0200 > +++ linux-2.6.0-test5-cpu/arch/i386/mm/init.c 2003-09-13 14:23:26.000000000 +0200 > @@ -436,8 +436,12 @@ > if (!mem_map) > BUG(); > #endif > - > + > +#ifdef CONFIG_CPU_686 > bad_ppro = ppro_with_ram_bug(); > +#else > + bad_ppro = 0; > +#endif >
If we boot a 386 kernel on a ppro with that bug, this goes bang.
> static void __init init_ifs(void) > { > + > +#if defined(CONFIG_CPU_K6) > amd_init_mtrr(); > +#endif > + > +#if defined(CONFIG_CPU_586) > cyrix_init_mtrr(); > +#endif > + > +#if defined(CONFIG_CPU_WINCHIP) || defined(CONFIG_CPU_CYRIXIII) || defined(CONFIG_CPU_VIAC3_2) > centaur_init_mtrr(); > +#endif > +
For the handful of bytes saved in the mtrr driver, I'm more concerned about ifdef noise, and the fact that we don't have a compile once-run everywhere MTRR driver anymore unless you pick your options right
Dave
-- Dave Jones http://www.codemonkey.org.uk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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