add pause support for the nix k10 architecture to marginally
improve power consumption, and to improve perfomance
under contention.

Reference: /n/atom/patch/applied2013/k10pause
Date: Sun Aug 25 19:21:28 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/archk10.c	Sun Aug 25 19:20:55 2013
+++ /sys/src/nix/k10/archk10.c	Sun Aug 25 19:20:56 2013
@@ -214,7 +214,7 @@
 
 	r = rdtsc();
 	for(t = r + m->cpumhz*µs; r < t; r = rdtsc())
-		;
+		pause();
 }
 
 void
@@ -224,5 +224,5 @@
 
 	r = rdtsc();
 	for(t = r + m->cpumhz*1000ull*ms; r < t; r = rdtsc())
-		;
+		pause();
 }
--- /sys/src/nix/k10/fns.h	Sun Aug 25 19:20:56 2013
+++ /sys/src/nix/k10/fns.h	Sun Aug 25 19:20:57 2013
@@ -85,6 +85,7 @@
 void	outs(int, ushort);
 void	outsl(int, void*, int);
 void	outss(int, void*, int);
+void	pause(void);
 int	pcicap(Pcidev*, int);
 int	pcicfgr16(Pcidev*, int);
 int	pcicfgr32(Pcidev*, int);
--- /sys/src/nix/k10/l64v.s	Sun Aug 25 19:20:58 2013
+++ /sys/src/nix/k10/l64v.s	Sun Aug 25 19:20:58 2013
@@ -354,6 +354,10 @@
 	MOVL	$0, AX				/* return 0 */
 	RET
 
+TEXT pause(SB), 1, $-4
+	PAUSE
+	RET
+
 TEXT hardhalt(SB), 1, $-4
 	STI
 	HLT