[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, 4 insertions, 3 deletions

diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index 0efad8aeb41a..4ec21037a361 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -291,10 +291,11 @@ void show_registers(struct pt_regs *regs)
         int i;
         int in_kernel = 1;
         unsigned long esp;
-        unsigned short ss;
+        unsigned short ss, gs;
 
         esp = (unsigned long) (&regs->esp);
         savesegment(ss, ss);
+        savesegment(gs, gs);
         if (user_mode_vm(regs)) {
                 in_kernel = 0;
                 esp = regs->esp;
@@ -313,8 +314,8 @@ void show_registers(struct pt_regs *regs)
                 regs->eax, regs->ebx, regs->ecx, regs->edx);
         printk(KERN_EMERG "esi: %08lx   edi: %08lx   ebp: %08lx   esp: %08lx\n",
                 regs->esi, regs->edi, regs->ebp, esp);
-        printk(KERN_EMERG "ds: %04x   es: %04x   ss: %04x\n",
-                regs->xds & 0xffff, regs->xes & 0xffff, ss);
+        printk(KERN_EMERG "ds: %04x   es: %04x   fs: %04x  gs: %04x  ss: %04x\n",
+               regs->xds & 0xffff, regs->xes & 0xffff, regs->xfs & 0xffff, gs, ss);
         printk(KERN_EMERG "Process %.*s (pid: %d, ti=%p task=%p task.ti=%p)",
                 TASK_COMM_LEN, current->comm, current->pid,
                 current_thread_info(), current, current->thread_info);