git: 9cb3288287ba - main - Skip TSC calibration if exact value known

The branch main has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=9cb3288287ba1b3c1d0ec891c552fc4b9472027e

commit 9cb3288287ba1b3c1d0ec891c552fc4b9472027e
Author:     Colin Percival <cperciva@FreeBSD.org>
AuthorDate: 2021-12-30 19:43:15 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2022-01-02 21:07:53 +0000

    Skip TSC calibration if exact value known
    
    It's possible that the "early" TSC calibration gave us a value which
    is known to be exact; in that case, skip the later re-calibration.
    
    MFC after:      2 weeks
    Differential Revision:  https://reviews.freebsd.org/D33695
---
 sys/x86/x86/tsc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
index ab8f94c2fc2d..534fdb5dd279 100644
--- a/sys/x86/x86/tsc.c
+++ b/sys/x86/x86/tsc.c
@@ -59,6 +59,7 @@ __FBSDID("$FreeBSD$");
 uint64_t	tsc_freq;
 int		tsc_is_invariant;
 int		tsc_perf_stat;
+static int	tsc_early_calib_exact;
 
 static eventhandler_tag tsc_levels_tag, tsc_pre_tag, tsc_post_tag;
 
@@ -133,6 +134,7 @@ tsc_freq_vmware(void)
 			tsc_freq = regs[0] | ((uint64_t)regs[1] << 32);
 	}
 	tsc_is_invariant = 1;
+	tsc_early_calib_exact = 1;
 }
 
 /*
@@ -709,6 +711,8 @@ tsc_calibrate(void)
 
 	if (tsc_disabled)
 		return;
+	if (tsc_early_calib_exact)
+		goto calibrated;
 
 	tc = atomic_load_ptr(&timecounter);
 
@@ -739,6 +743,7 @@ tsc_calibrate(void)
 	freq_khz = tc->tc_frequency * (tsc_end - tsc_start) / (t_end - t_start);
 
 	tsc_update_freq(freq_khz);
+calibrated:
 	tc_init(&tsc_timecounter);
 	set_cputicker(rdtsc, tsc_freq, !tsc_is_invariant);
 }