d/freebsd-dev
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86: Defer early TSC timecounter calibration to SI_SUB_CPU

Browse Source 
If we can't determine the TSC frequency using CPU registers, we need to
give a chance for Hyper-V drivers to register a timecounter (during
SI_SUB_HYPERVISOR) since an emulated 8254 might not be available.
Thus, split probe_tsc_freq() into early and late stages, and wait until
the latter to attempt calibration using a reference clock.

Fixes:		84369dd523 ("x86: Probe the TSC frequency earlier")
Reported and tested by:	khng, Shawn Webb
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D34444
This commit is contained in:
Mark Johnston 2022-03-04 19:34:43 -05:00
parent f7a6dccf42
commit 075e2779ac
1 changed files with 36 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
sys/x86/x86/tsc.c
View File

@ -240,7 +240,7 @@ tsc_freq_intel_brand(uint64_t *res)
}
static void
tsc_freq_8254(uint64_t *res)
tsc_freq_tc(uint64_t *res)
{
uint64_t tsc1, tsc2;
int64_t overhead;
@ -262,8 +262,15 @@ tsc_freq_8254(uint64_t *res)
tsc_freq = (tsc2 - tsc1 - overhead) * 10;
}
/*
* Try to determine the TSC frequency using CPUID or hypercalls. If successful,
* this lets use the TSC for early DELAY() calls instead of the 8254 timer,
* which may be unreliable or entirely absent on contemporary systems. However,
* avoid calibrating using the 8254 here so as to give hypervisors a chance to
* register a timecounter that can be used instead.
*/
static void
probe_tsc_freq(void)
probe_tsc_freq_early(void)
{
#ifdef __i386__
/* The TSC is known to be broken on certain CPUs. */
@ -364,7 +371,20 @@ probe_tsc_freq(void)
if (bootverbose)
printf("Early TSC frequency %juHz derived from CPUID\n",
(uintmax_t)tsc_freq);
} else if (tsc_skip_calibration) {
}
}
/*
* If we were unable to determine the TSC frequency via CPU registers, try
* to calibrate against a known clock.
*/
static void
probe_tsc_freq_late(void)
{
if (tsc_freq != 0)
return;
if (tsc_skip_calibration) {
/*
* Try to parse the brand string to obtain the nominal TSC
* frequency.
@ -380,15 +400,24 @@ probe_tsc_freq(void)
}
} else {
/*
* Calibrate against the 8254 PIT. This estimate will be
* refined later in tsc_calib().
* Calibrate against a timecounter or the 8254 PIT. This
* estimate will be refined later in tsc_calib().
*/
tsc_freq_8254(&tsc_freq);
tsc_freq_tc(&tsc_freq);
if (bootverbose)
printf(
"Early TSC frequency %juHz calibrated from 8254 PIT\n",
(uintmax_t)tsc_freq);
}
}
void
start_TSC(void)
{
if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled)
return;
probe_tsc_freq_late();
if (cpu_power_ecx & CPUID_PERF_STAT) {
/*
@ -401,13 +430,6 @@ probe_tsc_freq(void)
if (rdmsr(MSR_MPERF) > 0 && rdmsr(MSR_APERF) > 0)
tsc_perf_stat = 1;
}
}
void
start_TSC(void)
{
if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled)
return;
/*
* Inform CPU accounting about our boot-time clock rate. This will
@ -718,7 +740,7 @@ tsc_init(void)
if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled)
return;
probe_tsc_freq();
probe_tsc_freq_early();
}
/*