From 464d1a78fbf8cf6c7fd970e7b3e2db50a320ce28 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Tue, 13 Feb 2007 13:26:20 +0100 Subject: [PATCH] i386: Convert i386 PDA code to use %fs Convert the PDA code to use %fs rather than %gs as the segment for per-processor data. This is because some processors show a small but measurable performance gain for reloading a NULL segment selector (as %fs generally is in user-space) versus a non-NULL one (as %gs generally is). On modern processors the difference is very small, perhaps undetectable. Some old AMD "K6 3D+" processors are noticably slower when %fs is used rather than %gs; I have no idea why this might be, but I think they're sufficiently rare that it doesn't matter much. This patch also fixes the math emulator, which had not been adjusted to match the changed struct pt_regs. [frederik.deweerdt@gmail.com: fixit with gdb] [mingo@elte.hu: Fix KVM too] Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Andi Kleen Cc: Ian Campbell Acked-by: Ingo Molnar Acked-by: Zachary Amsden Cc: Eric Dumazet Signed-off-by: Frederik Deweerdt Signed-off-by: Andrew Morton --- arch/i386/math-emu/get_address.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) (limited to 'arch/i386/math-emu') diff --git a/arch/i386/math-emu/get_address.c b/arch/i386/math-emu/get_address.c index 9819b705efa4..2e2c51a8bd3a 100644 --- a/arch/i386/math-emu/get_address.c +++ b/arch/i386/math-emu/get_address.c @@ -56,15 +56,14 @@ static int reg_offset_vm86[] = { #define VM86_REG_(x) (*(unsigned short *) \ (reg_offset_vm86[((unsigned)x)]+(u_char *) FPU_info)) -/* These are dummy, fs and gs are not saved on the stack. */ -#define ___FS ___ds +/* This dummy, gs is not saved on the stack. */ #define ___GS ___ds static int reg_offset_pm[] = { offsetof(struct info,___cs), offsetof(struct info,___ds), offsetof(struct info,___es), - offsetof(struct info,___FS), + offsetof(struct info,___fs), offsetof(struct info,___GS), offsetof(struct info,___ss), offsetof(struct info,___ds) @@ -169,13 +168,10 @@ static long pm_address(u_char FPU_modrm, u_char segment, switch ( segment ) { - /* fs and gs aren't used by the kernel, so they still have their - user-space values. */ - case PREFIX_FS_-1: - /* N.B. - movl %seg, mem is a 2 byte write regardless of prefix */ - savesegment(fs, addr->selector); - break; + /* gs isn't used by the kernel, so it still has its + user-space value. */ case PREFIX_GS_-1: + /* N.B. - movl %seg, mem is a 2 byte write regardless of prefix */ savesegment(gs, addr->selector); break; default: -- cgit v1.2.2