[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>
diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index af8aabe..4a8f8a2 100644
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -89,14 +89,14 @@
unsigned long regno, unsigned long value)
{
switch (regno >> 2) {
- case FS:
+ case GS:
if (value && (value & 3) != 3)
return -EIO;
- child->thread.fs = value;
+ child->thread.gs = value;
return 0;
case DS:
case ES:
- case GS:
+ case FS:
if (value && (value & 3) != 3)
return -EIO;
value &= 0xffff;
@@ -112,7 +112,7 @@
value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
break;
}
- if (regno > ES*4)
+ if (regno > FS*4)
regno -= 1*4;
put_stack_long(child, regno, value);
return 0;
@@ -124,18 +124,18 @@
unsigned long retval = ~0UL;
switch (regno >> 2) {
- case FS:
- retval = child->thread.fs;
+ case GS:
+ retval = child->thread.gs;
break;
case DS:
case ES:
- case GS:
+ case FS:
case SS:
case CS:
retval = 0xffff;
/* fall through */
default:
- if (regno > ES*4)
+ if (regno > FS*4)
regno -= 1*4;
retval &= get_stack_long(child, regno);
}