From c05655bfda46e1ea6ddeee5a6c12ea44ddff28ec Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Thu, 17 Jan 2008 18:59:38 +0000
Subject: [PATCH] Use cpu_spinwait() (i.e., "pause") when spinning on rdtsc
 during DELAY().

MFC after:	1 week
---
 sys/amd64/isa/clock.c | 1 +
 sys/i386/isa/clock.c  | 1 +
 sys/isa/atrtc.c       | 1 +
 3 files changed, 3 insertions(+)

diff --git a/sys/amd64/isa/clock.c b/sys/amd64/isa/clock.c
index 2809828150b..32752672b7f 100644
--- a/sys/amd64/isa/clock.c
+++ b/sys/amd64/isa/clock.c
@@ -286,6 +286,7 @@ DELAY(int n)
 		start = rdtsc();
 		end = start + (tsc_freq * n) / 1000000;
 		do {
+			cpu_spinwait();
 			now = rdtsc();
 		} while (now < end || (now > start && end < start));
 		sched_unpin();
diff --git a/sys/i386/isa/clock.c b/sys/i386/isa/clock.c
index a67db3173a5..f31c7ea2eea 100644
--- a/sys/i386/isa/clock.c
+++ b/sys/i386/isa/clock.c
@@ -291,6 +291,7 @@ DELAY(int n)
 		start = rdtsc();
 		end = start + (tsc_freq * n) / 1000000;
 		do {
+			cpu_spinwait();
 			now = rdtsc();
 		} while (now < end || (now > start && end < start));
 		sched_unpin();
diff --git a/sys/isa/atrtc.c b/sys/isa/atrtc.c
index a67db3173a5..f31c7ea2eea 100644
--- a/sys/isa/atrtc.c
+++ b/sys/isa/atrtc.c
@@ -291,6 +291,7 @@ DELAY(int n)
 		start = rdtsc();
 		end = start + (tsc_freq * n) / 1000000;
 		do {
+			cpu_spinwait();
 			now = rdtsc();
 		} while (now < end || (now > start && end < start));
 		sched_unpin();