Timer¶
Because ACRN is a flexible, lightweight reference hypervisor, we provide limited timer management services:
Only the lapic tsc-deadline timer is supported as the clock source.
A timer can only be added on the logical CPU for a process or thread. Timer scheduling or timer migrating is not supported.
How It Works¶
When the system boots, we check that the hardware supports lapic tsc-deadline timer by checking CPUID.01H:ECX.TSC_Deadline[bit 24]. If support is missing, we output an error message and panic the hypervisor. If supported, we register the timer interrupt callback that raises a timer softirq on each logical CPU and sets the lapic timer mode to tsc-deadline timer mode by writing the local APIC LVT register.
Data Structures and APIs¶
Interfaces Design¶
-
void
initialize_timer(struct hv_timer *timer, timer_handle_t func, void *priv_data, uint64_t fire_tsc, uint64_t period_in_cycle)¶ Initialize a timer structure.
- Remark
Don’t initialize a timer twice if it has been added to the timer list after calling add_timer. If you want to, delete the timer from the list first.
- Return
None
- Parameters
[in] timer: Pointer to timer.[in] func: irq callback if time reached.[in] priv_data: func private data.[in] fire_tsc: tsc deadline to interrupt.[in] period_in_cycle: period of the periodic timer in unit of TSC cycles.
-
bool
timer_expired(const struct hv_timer *timer, uint64_t now, uint64_t *delta)¶ Check a timer whether expired.
- Parameters
[in] timer: Pointer to timer.[in] now: to compare.[in] delta: Pointer to return the delta (timeout - now) if timer is not expired.
- Return Value
true: if the timer is expired, false otherwise.
-
bool
timer_is_started(const struct hv_timer *timer)¶ Check if a timer is active (in the timer list) or not.
- Parameters
[in] timer: Pointer to timer.
- Return Value
true: if the timer is in timer list, false otherwise.
-
int32_t
add_timer(struct hv_timer *timer)¶ Add a timer.
- Remark
Don’t call it in the timer callback function or interrupt content.
- Parameters
[in] timer: Pointer to timer.
- Return Value
0: on success-EINVAL: timer has an invalid value
-
void
del_timer(struct hv_timer *timer)¶ Delete a timer.
- Return
None
- Remark
Don’t call it in the timer callback function or interrupt content.
- Parameters
[in] timer: Pointer to timer.
-
void
timer_init(void)¶ Initialize timer.
- Return
None
-
void
calibrate_tsc(void)¶ Calibrate Time Stamp Counter (TSC) frequency.
- Remark
Generic time related routines, e.g., cpu_tickrate(), us_to_ticks(), udelay(), etc., relies on this function being called earlier during system initialization.
- Return
None
-
uint64_t
cpu_ticks(void)¶ Read current CPU tick count.
- Remark
On x86, this is the Time Stamp Counter (TSC) value of the current logical CPU.
- Return
CPU ticks
-
uint32_t
cpu_tickrate(void)¶ Get CPU tick frequency in KHz.
- Remark
On x86, this is the Time Stamp Counter (TSC) frequency of the current logical CPU.
- Return
CPU frequency (KHz)
-
uint64_t
us_to_ticks(uint32_t us)¶ Convert micro seconds to CPU ticks.
- Return
CPU ticks
- Parameters
[in] us: micro seconds to convert
-
uint64_t
ticks_to_us(uint64_t ticks)¶ Convert CPU cycles to micro seconds.
- Return
microsecond
- Parameters
[in] ticks: CPU ticks to convert
-
uint64_t
ticks_to_ms(uint64_t ticks)¶ Convert CPU cycles to milli seconds.
- Return
millisecond
- Parameters
[in] ticks: CPU ticks to convert
-
void
udelay(uint32_t us)¶ Busy wait a few micro seconds.
- Parameters
[in] us: micro seconds to delay.
- Return Value
None: