Author: jkim
Date: Tue Apr 12 22:41:52 2011
New Revision: 220581
URL: http://svn.freebsd.org/changeset/base/220581
Log:
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.
Modified:
head/sys/x86/isa/clock.c
Modified: head/sys/x86/isa/clock.c
==============================================================================
--- head/sys/x86/isa/clock.c Tue Apr 12 22:22:01 2011 (r220580)
+++ head/sys/x86/isa/clock.c Tue Apr 12 22:41:52 2011 (r220581)
@@ -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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