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Use CPUID leaf 0x40000010 for local APIC freq

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Some VM systems announce the frequency of the local APIC via the
CPUID leaf 0x40000010.  Using this allows us to boot slightly
faster by avoiding the need for timer calibration.

Reviewed by:	markj
Sponsored by:	https://www.patreon.com/cperciva
This commit is contained in:
Colin Percival 2022-01-08 16:59:31 -08:00
parent 4a432614f6
commit de1292c6ff
1 changed files with 33 additions and 0 deletions
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33
sys/x86/x86/local_apic.c
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@ -1002,6 +1002,35 @@ native_lapic_disable_pmc(void)
#endif
}
static int
lapic_calibrate_initcount_cpuid_vm(void)
{
u_int regs[4];
uint64_t freq;
/* Get value from CPUID leaf if possible. */
if (vm_guest == VM_GUEST_NO)
return (false);
if (hv_high < 0x40000010)
return (false);
do_cpuid(0x40000010, regs);
freq = (uint64_t)(regs[1]) * 1000;
/* Pick timer divisor. */
lapic_timer_divisor = 2;
do {
if (freq / lapic_timer_divisor < APIC_TIMER_MAX_COUNT)
break;
lapic_timer_divisor <<= 1;
} while (lapic_timer_divisor <= 128);
if (lapic_timer_divisor > 128)
return (false);
/* Record divided frequency. */
count_freq = freq / lapic_timer_divisor;
return (true);
}
static uint64_t
cb_lapic_getcount(void)
{
@ -1014,6 +1043,9 @@ lapic_calibrate_initcount(struct lapic *la)
{
uint64_t freq;
if (lapic_calibrate_initcount_cpuid_vm())
goto done;
/* Calibrate the APIC timer frequency. */
lapic_timer_set_divisor(2);
lapic_timer_oneshot_nointr(la, APIC_TIMER_MAX_COUNT);
@ -1031,6 +1063,7 @@ lapic_calibrate_initcount(struct lapic *la)
if (lapic_timer_divisor > 128)
panic("lapic: Divisor too big");
count_freq = freq * 2 / lapic_timer_divisor;
done:
if (bootverbose) {
printf("lapic: Divisor %lu, Frequency %lu Hz\n",
lapic_timer_divisor, count_freq);