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calibrate lapic timer in native_lapic_setup

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The idea is to calibrate the LAPIC timer just once and only on boot,
given that [at present] the timer constants are global and shared
between all processors.

My primary motivation is to fix a panic that can happen when dynamically
switching to lapic timer.  The panic is caused by a recursion on
et_hw_mtx when printing the calibration results to console.  See the
review for the details of the panic.

Also, the code should become slightly simpler and easier to read.  The
previous code was racy too.  Multiple processors could start calibrating
the global constants concurrently, although that seems to have been
benign.

Reviewed by:	kib, mav, jhb
MFC after:	3 weeks
Differential Revision: https://reviews.freebsd.org/D15422
This commit is contained in:
Andriy Gapon 2018-05-15 16:56:30 +00:00
parent f2cf90e264
commit 7c5ccd2dce
1 changed files with 12 additions and 7 deletions
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19
sys/x86/x86/local_apic.c
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@ -206,6 +206,9 @@ SYSCTL_INT(_hw_apic, OID_AUTO, eoi_suppression, CTLFLAG_RD,
SYSCTL_INT(_hw_apic, OID_AUTO, timer_tsc_deadline, CTLFLAG_RD,
&lapic_timer_tsc_deadline, 0, "");
static void lapic_calibrate_initcount(struct lapic *la);
static void lapic_calibrate_deadline(struct lapic *la);
static uint32_t
lapic_read32(enum LAPIC_REGISTERS reg)
{
@ -787,6 +790,13 @@ native_lapic_setup(int boot)
intrcnt_add(buf, &la->la_timer_count);
}
/* Calibrate the timer parameters using BSP. */
if (boot && IS_BSP()) {
lapic_calibrate_initcount(la);
if (lapic_timer_tsc_deadline)
lapic_calibrate_deadline(la);
}
/* Setup the timer if configured. */
if (la->la_timer_mode != LAT_MODE_UNDEF) {
KASSERT(la->la_timer_period != 0, ("lapic%u: zero divisor",
@ -921,7 +931,7 @@ native_lapic_disable_pmc(void)
}
static void
lapic_calibrate_initcount(struct eventtimer *et, struct lapic *la)
lapic_calibrate_initcount(struct lapic *la)
{
u_long value;
@ -947,7 +957,7 @@ lapic_calibrate_initcount(struct eventtimer *et, struct lapic *la)
}
static void
lapic_calibrate_deadline(struct eventtimer *et, struct lapic *la __unused)
lapic_calibrate_deadline(struct lapic *la __unused)
{
if (bootverbose) {
@ -989,11 +999,6 @@ lapic_et_start(struct eventtimer *et, sbintime_t first, sbintime_t period)
struct lapic *la;
la = &lapics[PCPU_GET(apic_id)];
if (et->et_frequency == 0) {
lapic_calibrate_initcount(et, la);
if (lapic_timer_tsc_deadline)
lapic_calibrate_deadline(et, la);
}
if (period != 0) {
lapic_change_mode(et, la, LAT_MODE_PERIODIC);
la->la_timer_period = ((uint32_t)et->et_frequency * period) >>