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Kernel: Fix APIC timer calibration to be more accurate

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We were calibrating it to 260 instead of 250 ticks per second (being
off by one for the 1/10th second calibration time), resulting in
ticks of only ~3.6 ms instead of ~4ms. This gets us closer to ~4ms,
but because the APIC isn't nearly as precise as e.g. HPET, it will
only be a best effort. Then, use the higher precision reference
timer to more accurately calculate how many ticks we actually get
each second.

Also the frequency calculation was off, causing a "Frequency too slow"
error with VMware.

Fixes some problems observed in #5539
This commit is contained in:
Tom 2021-02-28 11:47:03 -07:00 committed by Andreas Kling
parent f66adbdd95
commit cdbd878a14
Notes: sideshowbarker 2024-07-18 21:50:04 +09:00 
Author: https://github.com/tomuta
Commit: https://github.com/SerenityOS/serenity/commit/cdbd878a145
Pull-request: https://github.com/SerenityOS/serenity/pull/5563
7 changed files with 64 additions and 23 deletions
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2
Kernel/Random.cpp
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@ -71,7 +71,7 @@ UNMAP_AFTER_INIT KernelRng::KernelRng()
klog() << "KernelRng: Using HPET as entropy source";
for (size_t i = 0; i < resource().pool_count * resource().reseed_threshold; ++i) {
u64 hpet_time = HPET::the().read_main_counter();
u64 hpet_time = HPET::the().read_main_counter_unsafe();
this->resource().add_random_event(hpet_time, i % 32);
}
} else {

33
Kernel/Time/APICTimer.cpp
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@ -65,28 +65,33 @@ UNMAP_AFTER_INIT bool APICTimer::calibrate(HardwareTimerBase& calibration_source
// temporarily replace the timer callbacks
const size_t ticks_in_100ms = calibration_source.ticks_per_second() / 10;
Atomic<size_t> calibration_ticks = 0;
Atomic<size_t, AK::memory_order_relaxed> calibration_ticks = 0;
#ifdef APIC_TIMER_MEASURE_CPU_CLOCK
volatile u64 start_tsc = 0, end_tsc = 0;
#endif
volatile u64 start_reference = 0, end_reference = 0;
volatile u32 start_apic_count = 0, end_apic_count = 0;
bool query_reference = calibration_source.can_query_raw();
auto original_source_callback = calibration_source.set_callback([&](const RegisterState&) {
u32 current_timer_count = apic.get_timer_current_count();
#ifdef APIC_TIMER_MEASURE_CPU_CLOCK
u64 current_tsc = supports_tsc ? read_tsc() : 0;
#endif
u64 current_reference = query_reference ? calibration_source.current_raw() : 0;
auto prev_tick = calibration_ticks.fetch_add(1, AK::memory_order_acq_rel);
auto prev_tick = calibration_ticks.fetch_add(1);
if (prev_tick == 0) {
#ifdef APIC_TIMER_MEASURE_CPU_CLOCK
start_tsc = current_tsc;
#endif
start_apic_count = current_timer_count;
} else if (prev_tick + 1 == ticks_in_100ms) {
start_reference = current_reference;
} else if (prev_tick + 1 == ticks_in_100ms + 1) {
#ifdef APIC_TIMER_MEASURE_CPU_CLOCK
end_tsc = current_tsc;
#endif
end_apic_count = current_timer_count;
end_reference = current_reference;
}
});
@ -102,7 +107,7 @@ UNMAP_AFTER_INIT bool APICTimer::calibrate(HardwareTimerBase& calibration_source
sti();
// Loop for about 100 ms
while (calibration_ticks.load(AK::memory_order_relaxed) < ticks_in_100ms)
while (calibration_ticks.load() <= ticks_in_100ms)
;
cli();
@ -112,25 +117,33 @@ UNMAP_AFTER_INIT bool APICTimer::calibrate(HardwareTimerBase& calibration_source
disable_local_timer();
if (query_reference) {
u64 one_tick_ns = calibration_source.raw_to_ns((end_reference - start_reference) / ticks_in_100ms);
m_frequency = (u32)(1000000000ull / one_tick_ns);
klog() << "APICTimer: Ticks per second: " << m_frequency << " (" << (one_tick_ns / 1000000) << "." << (one_tick_ns % 1000000) << "ms)";
} else {
// For now, assume the frequency is exactly the same
m_frequency = calibration_source.ticks_per_second();
klog() << "APICTimer: Ticks per second: " << m_frequency << " (assume same frequency as reference clock)";
}
auto delta_apic_count = start_apic_count - end_apic_count; // The APIC current count register decrements!
m_timer_period = (delta_apic_count * apic.get_timer_divisor()) / ticks_in_100ms;
auto apic_freq = (delta_apic_count * apic.get_timer_divisor()) / apic.get_timer_divisor();
u64 apic_freq = delta_apic_count * apic.get_timer_divisor() * 10;
klog() << "APICTimer: Bus clock speed: " << (apic_freq / 1000000) << "." << (apic_freq % 1000000) << " MHz";
if (apic_freq < 1000000) {
klog() << "APICTimer: Frequency too slow!";
return false;
}
klog() << "APICTimer: Bus clock speed: " << (apic_freq / 1000000) << "." << (apic_freq % 1000000) << " MHz";
#ifdef APIC_TIMER_MEASURE_CPU_CLOCK
if (supports_tsc) {
auto delta_tsc = end_tsc - start_tsc;
auto delta_tsc = (end_tsc - start_tsc) * 10;
klog() << "APICTimer: CPU clock speed: " << (delta_tsc / 1000000) << "." << (delta_tsc % 1000000) << " MHz";
}
#endif
// TODO: measure rather than assuming it matches?
m_frequency = calibration_source.ticks_per_second();
enable_local_timer();
return true;
}

31
Kernel/Time/HPET.cpp
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@ -38,7 +38,7 @@ namespace Kernel {
#define ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD 0x05F5E100
#define NANOSECOND_PERIOD_TO_HERTZ(x) 1000000000 / x
#define MEGAHERTZ_TO_HERTZ(x) (x / 1000000)
#define HERTZ_TO_MEGAHERTZ(x) (x / 1000000)
namespace HPETFlags {
enum class Attributes {
@ -220,7 +220,7 @@ void HPET::update_periodic_comparator_value()
// way to resume periodic timers properly because we reset the main counter
// and we can only write the period into the comparator value...
timer.capabilities = timer.capabilities | (u32)HPETFlags::TimerConfiguration::ValueSet;
u64 value = frequency() / comparator.ticks_per_second();
u64 value = ns_to_raw_counter_ticks(1000000000ull / comparator.ticks_per_second());
dbgln_if(HPET_DEBUG, "HPET: Update periodic comparator {} comparator value to {} main value was: {}",
comparator.comparator_number(),
value,
@ -250,11 +250,10 @@ void HPET::update_non_periodic_comparator_value(const HPETComparator& comparator
VERIFY_INTERRUPTS_DISABLED();
VERIFY(!comparator.is_periodic());
VERIFY(comparator.comparator_number() <= m_comparators.size());
auto& regs = registers();
auto& timer = regs.get_timer_by_index(comparator.comparator_number());
auto& timer = registers().get_timer_by_index(comparator.comparator_number());
u64 value = frequency() / comparator.ticks_per_second();
// NOTE: If the main counter passes this new value before we finish writing it, we will never receive an interrupt!
u64 new_counter_value = read_register_safe64(regs.main_counter_value) + value;
u64 new_counter_value = read_main_counter() + value;
timer.comparator_value.high = (u32)(new_counter_value >> 32);
timer.comparator_value.low = (u32)new_counter_value;
}
@ -262,7 +261,7 @@ void HPET::update_non_periodic_comparator_value(const HPETComparator& comparator
u64 HPET::update_time(u64& seconds_since_boot, u32& ticks_this_second, bool query_only)
{
// Should only be called by the time keeper interrupt handler!
u64 current_value = read_register_safe64(registers().main_counter_value);
u64 current_value = read_main_counter();
u64 delta_ticks = m_main_counter_drift;
if (current_value >= m_main_counter_last_read)
delta_ticks += current_value - m_main_counter_last_read;
@ -286,12 +285,17 @@ u64 HPET::update_time(u64& seconds_since_boot, u32& ticks_this_second, bool quer
return (delta_ticks * 1000000000ull) / ticks_per_second;
}
u64 HPET::read_main_counter() const
u64 HPET::read_main_counter_unsafe() const
{
auto& main_counter = registers().main_counter_value;
return ((u64)main_counter.high << 32) | (u64)main_counter.low;
}
u64 HPET::read_main_counter() const
{
return read_register_safe64(registers().main_counter_value);
}
void HPET::enable_periodic_interrupt(const HPETComparator& comparator)
{
#if HPET_DEBUG
@ -405,10 +409,15 @@ HPETRegistersBlock& HPET::registers()
return *(HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
}
u64 HPET::calculate_ticks_in_nanoseconds() const
u64 HPET::raw_counter_ticks_to_ns(u64 raw_ticks) const
{
// ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD == 100 nanoseconds
return ((u64)registers().capabilities.main_counter_tick_period * 100ull) / ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD;
return (raw_ticks * (u64)registers().capabilities.main_counter_tick_period * 100ull) / ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD;
}
u64 HPET::ns_to_raw_counter_ticks(u64 ns) const
{
return (ns * 1000000ull) / (u64)registers().capabilities.main_counter_tick_period;
}
UNMAP_AFTER_INIT HPET::HPET(PhysicalAddress acpi_hpet)
@ -438,8 +447,8 @@ UNMAP_AFTER_INIT HPET::HPET(PhysicalAddress acpi_hpet)
global_disable();
m_frequency = NANOSECOND_PERIOD_TO_HERTZ(calculate_ticks_in_nanoseconds());
klog() << "HPET: frequency " << m_frequency << " Hz (" << MEGAHERTZ_TO_HERTZ(m_frequency) << " MHz) resolution: " << calculate_ticks_in_nanoseconds() << "ns";
m_frequency = NANOSECOND_PERIOD_TO_HERTZ(raw_counter_ticks_to_ns(1));
klog() << "HPET: frequency " << m_frequency << " Hz (" << HERTZ_TO_MEGAHERTZ(m_frequency) << " MHz) resolution: " << raw_counter_ticks_to_ns(1) << "ns";
VERIFY(regs.capabilities.main_counter_tick_period <= ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD);
// Reset the counter, just in case... (needs to match m_main_counter_last_read)

5
Kernel/Time/HPET.h
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@ -46,6 +46,8 @@ public:
static HPET& the();
u64 frequency() const { return m_frequency; }
u64 raw_counter_ticks_to_ns(u64) const;
u64 ns_to_raw_counter_ticks(u64) const;
const NonnullRefPtrVector<HPETComparator>& comparators() const { return m_comparators; }
void disable(const HPETComparator&);
@ -60,6 +62,7 @@ public:
void disable_periodic_interrupt(const HPETComparator& comparator);
u64 update_time(u64& seconds_since_boot, u32& ticks_this_second, bool query_only);
u64 read_main_counter_unsafe() const;
u64 read_main_counter() const;
Vector<unsigned> capable_interrupt_numbers(u8 comparator_number);
@ -75,7 +78,7 @@ private:
bool is_periodic_capable(u8 comparator_number);
void set_comparators_to_optimal_interrupt_state(size_t timers_count);
u64 calculate_ticks_in_nanoseconds() const;
u64 nanoseconds_to_raw_ticks() const;
PhysicalAddress find_acpi_hpet_registers_block();
explicit HPET(PhysicalAddress acpi_hpet);

10
Kernel/Time/HPETComparator.cpp
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@ -138,4 +138,14 @@ size_t HPETComparator::calculate_nearest_possible_frequency(size_t frequency) co
return frequency;
}
u64 HPETComparator::current_raw() const
{
return HPET::the().read_main_counter();
}
u64 HPETComparator::raw_to_ns(u64 raw_delta) const
{
return HPET::the().raw_counter_ticks_to_ns(raw_delta);
}
}

3
Kernel/Time/HPETComparator.h
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@ -51,6 +51,9 @@ public:
virtual void set_periodic() override;
virtual void set_non_periodic() override;
virtual void disable() override;
virtual bool can_query_raw() const override { return true; }
virtual u64 current_raw() const override;
virtual u64 raw_to_ns(u64) const override;
virtual void reset_to_default_ticks_per_second() override;
virtual bool try_to_set_frequency(size_t frequency) override;

3
Kernel/Time/HardwareTimer.h
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@ -65,6 +65,9 @@ public:
virtual void set_non_periodic() = 0;
virtual void disable() = 0;
virtual u32 frequency() const = 0;
virtual bool can_query_raw() const { return false; }
virtual u64 current_raw() const { return 0; }
virtual u64 raw_to_ns(u64) const { return 0; }
virtual size_t ticks_per_second() const = 0;