Add support for per-rthread base-offset for the %fs selector on amd64.

Add pcb_fsbase to the PCB for tracking what the value for the thread
is, and ci_cur_fsbase to struct cpu_info for tracking the CPU's current
value for FS.base, then on return to user-space, skip the setting if the
CPU has the right value already.  Non-threaded processes without TLS leave
FS.base zero, which can be conveniently optimized: setting %fs zeros
FS.base for fewer cycles than wrmsr.

ok kettenis@

1 files changed, 2 insertions, 1 deletions

diff --git a/sys/arch/amd64/include/cpu.h b/sys/arch/amd64/include/cpu.h
index 260212f10a9..53e063ae551 100644
--- a/sys/arch/amd64/include/cpu.h
+++ b/sys/arch/amd64/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.63 2011/03/23 16:54:34 pirofti Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.64 2011/04/05 21:14:00 guenther Exp $	*/
 /*	$NetBSD: cpu.h,v 1.1 2003/04/26 18:39:39 fvdl Exp $	*/
 
 /*-
@@ -72,6 +72,7 @@ struct cpu_info {
 	u_int32_t ci_randseed;
 
 	u_int64_t ci_scratch;
+	u_int64_t ci_cur_fsbase;
 
 	struct proc *ci_fpcurproc;
 	struct proc *ci_fpsaveproc;