From 2092a06579f29873b4c1f7e4a294dfc71e455844 Mon Sep 17 00:00:00 2001
From: jkim <jkim@FreeBSD.org>
Date: Tue, 12 Apr 2011 22:41:52 +0000
Subject: Do not use TSC for DELAY(9) if it not P-state invariant to avoid
 possible foot-shooting.  DELAY() becomes unreliable when TSC frequency varies
 wildly, especially cpufreq(4) and powerd(8) are used at the same time.

---
 sys/x86/isa/clock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'sys/x86/isa')

diff --git a/sys/x86/isa/clock.c b/sys/x86/isa/clock.c
index d82dad7..5556ee6 100644
--- a/sys/x86/isa/clock.c
+++ b/sys/x86/isa/clock.c
@@ -263,7 +263,7 @@ delay_tc(int n)
 
 	tc = timecounter;
 	freq = atomic_load_acq_64(&tsc_freq);
-	if (freq != 0) {
+	if (tsc_is_invariant && freq != 0) {
 		func = get_tsc;
 		mask = ~0u;
 	} else {
-- 
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