[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 <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Ian Campbell <Ian.Campbell@XenSource.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Zachary Amsden <zach@vmware.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/asm-i386/elf.h b/include/asm-i386/elf.h
index 369035dfe4b6..8d33c9bb7c1c 100644
--- a/include/asm-i386/elf.h
+++ b/include/asm-i386/elf.h
@@ -90,8 +90,8 @@ typedef struct user_fxsr_struct elf_fpxregset_t;
         pr_reg[6] = regs->eax;                          \
         pr_reg[7] = regs->xds;                          \
         pr_reg[8] = regs->xes;                          \
-        savesegment(fs,pr_reg[9]);                      \
-        pr_reg[10] = regs->xgs;                         \
+        pr_reg[9] = regs->xfs;                          \
+        savesegment(gs,pr_reg[10]);                     \
         pr_reg[11] = regs->orig_eax;                    \
         pr_reg[12] = regs->eip;                         \
         pr_reg[13] = regs->xcs;                         \