[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, 6 insertions, 6 deletions

diff --git a/include/asm-i386/pda.h b/include/asm-i386/pda.h
index 2ba2736aa109..b12d59a318b7 100644
--- a/include/asm-i386/pda.h
+++ b/include/asm-i386/pda.h
@@ -39,19 +39,19 @@ extern struct i386_pda _proxy_pda;
                 if (0) { T__ tmp__; tmp__ = (val); }                    \
                 switch (sizeof(_proxy_pda.field)) {                     \
                 case 1:                                                 \
-                        asm(op "b %1,%%gs:%c2"                          \
+                        asm(op "b %1,%%fs:%c2"                          \
                             : "+m" (_proxy_pda.field)                   \
                             :"ri" ((T__)val),                           \
                              "i"(pda_offset(field)));                   \
                         break;                                          \
                 case 2:                                                 \
-                        asm(op "w %1,%%gs:%c2"                          \
+                        asm(op "w %1,%%fs:%c2"                          \
                             : "+m" (_proxy_pda.field)                   \
                             :"ri" ((T__)val),                           \
                              "i"(pda_offset(field)));                   \
                         break;                                          \
                 case 4:                                                 \
-                        asm(op "l %1,%%gs:%c2"                          \
+                        asm(op "l %1,%%fs:%c2"                          \
                             : "+m" (_proxy_pda.field)                   \
                             :"ri" ((T__)val),                           \
                              "i"(pda_offset(field)));                   \
@@ -65,19 +65,19 @@ extern struct i386_pda _proxy_pda;
                 typeof(_proxy_pda.field) ret__;                         \
                 switch (sizeof(_proxy_pda.field)) {                     \
                 case 1:                                                 \
-                        asm(op "b %%gs:%c1,%0"                          \
+                        asm(op "b %%fs:%c1,%0"                          \
                             : "=r" (ret__)                              \
                             : "i" (pda_offset(field)),                  \
                               "m" (_proxy_pda.field));                  \
                         break;                                          \
                 case 2:                                                 \
-                        asm(op "w %%gs:%c1,%0"                          \
+                        asm(op "w %%fs:%c1,%0"                          \
                             : "=r" (ret__)                              \
                             : "i" (pda_offset(field)),                  \
                               "m" (_proxy_pda.field));                  \
                         break;                                          \
                 case 4:                                                 \
-                        asm(op "l %%gs:%c1,%0"                          \
+                        asm(op "l %%fs:%c1,%0"                          \
                             : "=r" (ret__)                              \
                             : "i" (pda_offset(field)),                  \
                               "m" (_proxy_pda.field));                  \