[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, 8 insertions, 8 deletions

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index af8aabe85800..4a8f8a259723 100644
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -89,14 +89,14 @@ static int putreg(struct task_struct *child,
         unsigned long regno, unsigned long value)
 {
         switch (regno >> 2) {
-                case FS:
+                case GS:
                         if (value && (value & 3) != 3)
                                 return -EIO;
-                        child->thread.fs = value;
+                        child->thread.gs = value;
                         return 0;
                 case DS:
                 case ES:
-                case GS:
+                case FS:
                         if (value && (value & 3) != 3)
                                 return -EIO;
                         value &= 0xffff;
@@ -112,7 +112,7 @@ static int putreg(struct task_struct *child,
                         value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
                         break;
         }
-        if (regno > ES*4)
+        if (regno > FS*4)
                 regno -= 1*4;
         put_stack_long(child, regno, value);
         return 0;
@@ -124,18 +124,18 @@ static unsigned long getreg(struct task_struct *child,
         unsigned long retval = ~0UL;
 
         switch (regno >> 2) {
-                case FS:
-                        retval = child->thread.fs;
+                case GS:
+                        retval = child->thread.gs;
                         break;
                 case DS:
                 case ES:
-                case GS:
+                case FS:
                 case SS:
                 case CS:
                         retval = 0xffff;
                         /* fall through */
                 default:
-                        if (regno > ES*4)
+                        if (regno > FS*4)
                                 regno -= 1*4;
                         retval &= get_stack_long(child, regno);
         }