replace the portable function "mwait" with monmwait.  monmwait(9)
has the full definition, but it essentially waits for a bit of memory to
change from a particular value

Reference: /n/atom/patch/applied2013/monmwait
Date: Wed Sep 18 17:20:05 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/fns.h	Wed Sep 18 17:20:00 2013
+++ /sys/src/nix/k10/fns.h	Wed Sep 18 17:20:00 2013
@@ -150,7 +150,7 @@
 /*
  * archk10.c
  */
-void k10mwait(void*);
+void monmwait(void*, uintptr);
 
 /*
  * i8259.c
--- /sys/src/nix/k10/l64v.s	Wed Sep 18 17:20:00 2013
+++ /sys/src/nix/k10/l64v.s	Wed Sep 18 17:20:00 2013
@@ -369,7 +369,7 @@
 /*
  * uintptr monmwait(void*, uintptr)
  */
-TEXT	k10mwait(SB),1,$16
+TEXT	monmwait(SB),1,$16
 	MOVQ	val+8(FP), BX
 
 _mmstart:
--- /sys/src/nix/k10/archk10.c	Wed Sep 18 17:20:00 2013
+++ /sys/src/nix/k10/archk10.c	Wed Sep 18 17:20:00 2013
@@ -12,8 +12,8 @@
 	u32int info[4];
 
 	cpuid(1, 0, info);
-	if(info[2] & 8)
-		mwait = k10mwait;
+	if((info[2] & 8) == 0)
+		panic("k10archinit: mwait required");
 }
 
 static int
--- /sys/src/nix/port/taslock.c	Wed Sep 18 17:20:00 2013
+++ /sys/src/nix/port/taslock.c	Wed Sep 18 17:20:00 2013
@@ -233,12 +233,3 @@
 		up->lastilock = nil;
 	splx(pl);
 }
-
-void
-portmwait(void *value)
-{
-	while (*(void**)value == nil)
-		pause();
-}
-
-void (*mwait)(void *) = portmwait;
--- /sys/man/9/monmwait	Thu Jan  1 00:00:00 1970
+++ /sys/man/9/monmwait	Wed Sep 18 17:20:00 2013
@@ -0,0 +1,50 @@
+.TH MONMWAIT 9
+.SH NAME
+monmwait \- wait for memory write
+.SH SYNOPSIS
+.ta \w'\fLvoid 'u
+.B
+void	monmwait(void *adr, uintmem oldval)
+.SH DESCRIPTION
+Wait for the value pointed to by
+.B adr
+to change from
+.B oldval
+in the most power- and bus-cycle efficient way afforded by
+the architecture.
+.PP
+Since no lock is involved,
+.I monmwait
+may not be used where ABA might be a problem.  This function will
+never  miss a (persistent) change, but may return before the value has
+changed, for example if interrupted, or if a “nearby” memory location
+has been written.
+.I Nearby
+is dependent on the architecture and
+implementation.  On current x86 platforms,
+.I nearby
+means in the
+same cacheline.
+.PP
+The minimal correct implementation would be a no-op.
+On x86 machines, the implementation uses
+the
+.SM MONITOR
+and
+.SM MWAIT
+instructions.
+.SH EXAMPLES
+Application processors can use
+.I monmwait
+while waiting for release to keep the fans from spooling up:
+.IP
+.EX
+while(!active.thunderbirdsarego)
+	monmwait(&active.thunderbirdsarego, 0);
+.EE
+.PP
+.SH SOURCE
+.B /sys/src/nix/k10/l64v.s
+.SH SEE ALSO
+.IR atom (2),
+.IR lock (9)