[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>

5 files changed, 14 insertions, 14 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;                         \
diff --git a/include/asm-i386/mmu_context.h b/include/asm-i386/mmu_context.h
index 68ff102d6f5e..e6aa30f8de5b 100644
--- a/include/asm-i386/mmu_context.h
+++ b/include/asm-i386/mmu_context.h
@@ -63,7 +63,7 @@ static inline void switch_mm(struct mm_struct *prev,
 }
 
 #define deactivate_mm(tsk, mm)                  \
-        asm("movl %0,%%fs": :"r" (0));
+        asm("movl %0,%%gs": :"r" (0));
 
 #define activate_mm(prev, next) \
         switch_mm((prev),(next),NULL)
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));                  \
diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 359f10b54f59..11bf899de8aa 100644
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -424,7 +424,7 @@ struct thread_struct {
         .vm86_info = NULL,                                              \
         .sysenter_cs = __KERNEL_CS,                                     \
         .io_bitmap_ptr = NULL,                                          \
-        .gs = __KERNEL_PDA,                                             \
+        .fs = __KERNEL_PDA,                                             \
 }
 
 /*
@@ -442,8 +442,8 @@ struct thread_struct {
 }
 
 #define start_thread(regs, new_eip, new_esp) do {               \
-        __asm__("movl %0,%%fs": :"r" (0));                      \
-        regs->xgs = 0;                                          \
+        __asm__("movl %0,%%gs": :"r" (0));                      \
+        regs->xfs = 0;                                          \
         set_fs(USER_DS);                                        \
         regs->xds = __USER_DS;                                  \
         regs->xes = __USER_DS;                                  \
diff --git a/include/asm-i386/ptrace.h b/include/asm-i386/ptrace.h
index bdbc894339b4..1646996c73da 100644
--- a/include/asm-i386/ptrace.h
+++ b/include/asm-i386/ptrace.h
@@ -16,8 +16,8 @@ struct pt_regs {
         long eax;
         int  xds;
         int  xes;
-        /* int  xfs; */
-        int  xgs;
+        int  xfs;
+        /* int  xgs; */
         long orig_eax;
         long eip;
         int  xcs;