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clockevents: Provide support for clocksource coupled comparators

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Some clockevent devices are coupled to the system clocksource by
implementing a less than or equal comparator which compares the programmed
absolute expiry time against the underlying time counter.

The timekeeping core provides a function to convert and absolute
CLOCK_MONOTONIC based expiry time to a absolute clock cycles time which can
be directly fed into the comparator. That spares two time reads in the next
event progamming path, one to convert the absolute nanoseconds time to a
delta value and the other to convert the delta value back to a absolute
time value suitable for the comparator.

Provide a new clocksource callback which takes the absolute cycle value and
wire it up in clockevents_program_event(). Similar to clocksources allow
architectures to inline the rearm operation.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163430.010425428@kernel.org
This commit is contained in:
Thomas Gleixner
2026-02-24 17:36:45 +01:00
committed by Peter Zijlstra
parent cd38bdb8e6
commit 89f951a1e8
3 changed files with 48 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/clockchips.h
View File

@@ -43,8 +43,9 @@ enum clock_event_state {
/*
* Clock event features
*/
# define CLOCK_EVT_FEAT_PERIODIC 0x000001
# define CLOCK_EVT_FEAT_ONESHOT 0x000002
# define CLOCK_EVT_FEAT_PERIODIC 0x000001
# define CLOCK_EVT_FEAT_ONESHOT 0x000002
# define CLOCK_EVT_FEAT_CLOCKSOURCE_COUPLED 0x000004
/*
* x86(64) specific (mis)features:
@@ -100,6 +101,7 @@ struct clock_event_device {
void (*event_handler)(struct clock_event_device *);
int (*set_next_event)(unsigned long evt, struct clock_event_device *);
int (*set_next_ktime)(ktime_t expires, struct clock_event_device *);
void (*set_next_coupled)(u64 cycles, struct clock_event_device *);
ktime_t next_event;
u64 max_delta_ns;
u64 min_delta_ns;
@@ -107,6 +109,7 @@ struct clock_event_device {
u32 shift;
enum clock_event_state state_use_accessors;
unsigned int features;
enum clocksource_ids cs_id;
unsigned long retries;
int (*set_state_periodic)(struct clock_event_device *);

4
kernel/time/Kconfig
View File

@@ -50,6 +50,10 @@ config GENERIC_CLOCKEVENTS_MIN_ADJUST
config GENERIC_CLOCKEVENTS_COUPLED
bool
config GENERIC_CLOCKEVENTS_COUPLED_INLINE
select GENERIC_CLOCKEVENTS_COUPLED
bool
# Generic update of CMOS clock
config GENERIC_CMOS_UPDATE
bool

44
kernel/time/clockevents.c
View File

@@ -292,6 +292,38 @@ static int clockevents_program_min_delta(struct clock_event_device *dev)
#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */
#ifdef CONFIG_GENERIC_CLOCKEVENTS_COUPLED
#ifdef CONFIG_GENERIC_CLOCKEVENTS_COUPLED_INLINE
#include <asm/clock_inlined.h>
#else
static __always_inline void
arch_inlined_clockevent_set_next_coupled(u64 u64 cycles, struct clock_event_device *dev) { }
#endif
static inline bool clockevent_set_next_coupled(struct clock_event_device *dev, ktime_t expires)
{
u64 cycles;
if (unlikely(!(dev->features & CLOCK_EVT_FEAT_CLOCKSOURCE_COUPLED)))
return false;
if (unlikely(!ktime_expiry_to_cycles(dev->cs_id, expires, &cycles)))
return false;
if (IS_ENABLED(CONFIG_GENERIC_CLOCKEVENTS_COUPLED_INLINE))
arch_inlined_clockevent_set_next_coupled(cycles, dev);
else
dev->set_next_coupled(cycles, dev);
return true;
}
#else
static inline bool clockevent_set_next_coupled(struct clock_event_device *dev, ktime_t expires)
{
return false;
}
#endif
/**
* clockevents_program_event - Reprogram the clock event device.
* @dev: device to program
@@ -300,11 +332,10 @@ static int clockevents_program_min_delta(struct clock_event_device *dev)
*
* Returns 0 on success, -ETIME when the event is in the past.
*/
int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
bool force)
int clockevents_program_event(struct clock_event_device *dev, ktime_t expires, bool force)
{
unsigned long long clc;
int64_t delta;
u64 cycles;
int rc;
if (WARN_ON_ONCE(expires < 0))
@@ -323,6 +354,9 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
if (unlikely(dev->features & CLOCK_EVT_FEAT_HRTIMER))
return dev->set_next_ktime(expires, dev);
if (likely(clockevent_set_next_coupled(dev, expires)))
return 0;
delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
if (delta <= 0)
return force ? clockevents_program_min_delta(dev) : -ETIME;
@@ -330,8 +364,8 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
delta = min(delta, (int64_t) dev->max_delta_ns);
delta = max(delta, (int64_t) dev->min_delta_ns);
clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
rc = dev->set_next_event((unsigned long) clc, dev);
cycles = ((u64)delta * dev->mult) >> dev->shift;
rc = dev->set_next_event((unsigned long) cycles, dev);
return (rc && force) ? clockevents_program_min_delta(dev) : rc;
}