[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, 16 insertions, 16 deletions

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 5e47683fc63a..8c6a22a42d2e 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -30,7 +30,7 @@
  *      18(%esp) - %eax
  *      1C(%esp) - %ds
  *      20(%esp) - %es
- *      24(%esp) - %gs
+ *      24(%esp) - %fs
  *      28(%esp) - orig_eax
  *      2C(%esp) - %eip
  *      30(%esp) - %cs
@@ -99,9 +99,9 @@ VM_MASK		= 0x00020000
 
 #define SAVE_ALL \
         cld; \
-        pushl %gs; \
+        pushl %fs; \
         CFI_ADJUST_CFA_OFFSET 4;\
-        /*CFI_REL_OFFSET gs, 0;*/\
+        /*CFI_REL_OFFSET fs, 0;*/\
         pushl %es; \
         CFI_ADJUST_CFA_OFFSET 4;\
         /*CFI_REL_OFFSET es, 0;*/\
@@ -133,7 +133,7 @@ VM_MASK		= 0x00020000
         movl %edx, %ds; \
         movl %edx, %es; \
         movl $(__KERNEL_PDA), %edx; \
-        movl %edx, %gs
+        movl %edx, %fs
 
 #define RESTORE_INT_REGS \
         popl %ebx;      \
@@ -166,9 +166,9 @@ VM_MASK		= 0x00020000
 2:      popl %es;       \
         CFI_ADJUST_CFA_OFFSET -4;\
         /*CFI_RESTORE es;*/\
-3:      popl %gs;       \
+3:      popl %fs;       \
         CFI_ADJUST_CFA_OFFSET -4;\
-        /*CFI_RESTORE gs;*/\
+        /*CFI_RESTORE fs;*/\
 .pushsection .fixup,"ax";       \
 4:      movl $0,(%esp); \
         jmp 1b;         \
@@ -349,11 +349,11 @@ sysenter_past_esp:
         movl PT_OLDESP(%esp), %ecx
         xorl %ebp,%ebp
         TRACE_IRQS_ON
-1:      mov  PT_GS(%esp), %gs
+1:      mov  PT_FS(%esp), %fs
         ENABLE_INTERRUPTS_SYSEXIT
         CFI_ENDPROC
 .pushsection .fixup,"ax"
-2:      movl $0,PT_GS(%esp)
+2:      movl $0,PT_FS(%esp)
         jmp 1b
 .section __ex_table,"a"
         .align 4
@@ -550,7 +550,7 @@ syscall_badsys:
 
 #define FIXUP_ESPFIX_STACK \
         /* since we are on a wrong stack, we cant make it a C code :( */ \
-        movl %gs:PDA_cpu, %ebx; \
+        movl %fs:PDA_cpu, %ebx; \
         PER_CPU(cpu_gdt_descr, %ebx); \
         movl GDS_address(%ebx), %ebx; \
         GET_DESC_BASE(GDT_ENTRY_ESPFIX_SS, %ebx, %eax, %ax, %al, %ah); \
@@ -632,7 +632,7 @@ KPROBE_ENTRY(page_fault)
         CFI_ADJUST_CFA_OFFSET 4
         ALIGN
 error_code:
-        /* the function address is in %gs's slot on the stack */
+        /* the function address is in %fs's slot on the stack */
         pushl %es
         CFI_ADJUST_CFA_OFFSET 4
         /*CFI_REL_OFFSET es, 0*/
@@ -661,20 +661,20 @@ error_code:
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET ebx, 0
         cld
-        pushl %gs
+        pushl %fs
         CFI_ADJUST_CFA_OFFSET 4
-        /*CFI_REL_OFFSET gs, 0*/
+        /*CFI_REL_OFFSET fs, 0*/
         movl $(__KERNEL_PDA), %ecx
-        movl %ecx, %gs
+        movl %ecx, %fs
         UNWIND_ESPFIX_STACK
         popl %ecx
         CFI_ADJUST_CFA_OFFSET -4
         /*CFI_REGISTER es, ecx*/
-        movl PT_GS(%esp), %edi          # get the function address
+        movl PT_FS(%esp), %edi          # get the function address
         movl PT_ORIG_EAX(%esp), %edx    # get the error code
         movl $-1, PT_ORIG_EAX(%esp)     # no syscall to restart
-        mov  %ecx, PT_GS(%esp)
-        /*CFI_REL_OFFSET gs, ES*/
+        mov  %ecx, PT_FS(%esp)
+        /*CFI_REL_OFFSET fs, ES*/
         movl $(__USER_DS), %ecx
         movl %ecx, %ds
         movl %ecx, %es