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Index: head/sys/x86/x86/delay.c
===================================================================
--- head/sys/x86/x86/delay.c
+++ head/sys/x86/x86/delay.c
@@ -51,11 +51,23 @@
#include <machine/cpu.h>
#include <x86/init.h>
-static u_int
-get_tsc(__unused struct timecounter *tc)
+static void
+delay_tsc(int n)
{
+ uint64_t end, now;
- return (rdtsc32());
+ /*
+ * Pin the current thread ensure correct behavior if the TSCs
+ * on different CPUs are not in sync.
+ */
+ sched_pin();
+ now = rdtsc();
+ end = now + tsc_freq * n / 1000000;
+ do {
+ cpu_spinwait();
+ now = rdtsc();
+ } while (now < end);
+ sched_unpin();
}
static int
@@ -66,22 +78,24 @@
uint64_t end, freq, now;
u_int last, mask, u;
- tc = timecounter;
- freq = atomic_load_acq_64(&tsc_freq);
- if (tsc_is_invariant && freq != 0) {
- func = get_tsc;
- mask = ~0u;
- } else {
- if (tc->tc_quality <= 0)
- return (0);
- func = tc->tc_get_timecount;
- mask = tc->tc_counter_mask;
- freq = tc->tc_frequency;
+ /*
+ * Only use the TSC if it is P-state invariant. If the TSC is
+ * not P-state invariant and the CPU is not running at the
+ * "full" P-state, then the TSC will increment at some rate
+ * less than tsc_freq and delay_tsc() will wait too long.
+ */
+ if (tsc_is_invariant && tsc_freq != 0) {
+ delay_tsc(n);
+ return (1);
}
+ tc = timecounter;
+ if (tc->tc_quality <= 0)
+ return (0);
+ func = tc->tc_get_timecount;
+ mask = tc->tc_counter_mask;
+ freq = tc->tc_frequency;
now = 0;
end = freq * n / 1000000;
- if (func == get_tsc)
- sched_pin();
last = func(tc) & mask;
do {
cpu_spinwait();
@@ -92,8 +106,6 @@
now += u - last;
last = u;
} while (now < end);
- if (func == get_tsc)
- sched_unpin();
return (1);
}

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