[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/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index af1d53344993..b85cfa3ce1dd 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/arch/i386/kernel/kprobes.c
@@ -363,7 +363,7 @@ no_kprobe:
                         "       pushf\n"
                         /* skip cs, eip, orig_eax */
                         "       subl $12, %esp\n"
-                        "       pushl %gs\n"
+                        "       pushl %fs\n"
                         "       pushl %ds\n"
                         "       pushl %es\n"
                         "       pushl %eax\n"
@@ -387,7 +387,7 @@ no_kprobe:
                         "       popl %edi\n"
                         "       popl %ebp\n"
                         "       popl %eax\n"
-                        /* skip eip, orig_eax, es, ds, gs */
+                        /* skip eip, orig_eax, es, ds, fs */
                         "       addl $20, %esp\n"
                         "       popf\n"
                         "       ret\n");