[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/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 1e640b899175..fd4e91734388 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1879,12 +1879,6 @@ again:
 
         asm ("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
 
-        /*
-         * Profile KVM exit RIPs:
-         */
-        if (unlikely(prof_on == KVM_PROFILING))
-                profile_hit(KVM_PROFILING, (void *)vmcs_readl(GUEST_RIP));
-
         kvm_run->exit_type = 0;
         if (fail) {
                 kvm_run->exit_type = KVM_EXIT_TYPE_FAIL_ENTRY;
@@ -1907,6 +1901,12 @@ again:
 
                         reload_tss();
                 }
+                /*
+                 * Profile KVM exit RIPs:
+                 */
+                if (unlikely(prof_on == KVM_PROFILING))
+                        profile_hit(KVM_PROFILING, (void *)vmcs_readl(GUEST_RIP));
+
                 vcpu->launched = 1;
                 kvm_run->exit_type = KVM_EXIT_TYPE_VM_EXIT;
                 r = kvm_handle_exit(kvm_run, vcpu);