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time: Introduce auxiliary POSIX clocks 

To support auxiliary timekeeping and the related user space interfaces,
it's required to define a clock ID range for them.

Reserve 8 auxiliary clock IDs after the regular timekeeping clock ID space.

This is the maximum number of auxiliary clocks the kernel can support. The actual
number of supported clocks depends obviously on the presence of related devices
and might be constraint by the available VDSO space.

Add the corresponding timekeeper IDs as well.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250519083025.905800695@linutronix.de
This commit is contained in:
Anna-Maria Behnsen 2025-05-19 10:33:20 +02:00 committed by Thomas Gleixner
parent f12b45862c
commit 9094c72c3d
3 changed files with 32 additions and 4 deletions
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6
include/linux/timekeeper_internal.h
View File

@ -14,10 +14,16 @@
/**
* timekeeper_ids - IDs for various time keepers in the kernel
* @TIMEKEEPER_CORE: The central core timekeeper managing system time
* @TIMEKEEPER_AUX_FIRST: The first AUX timekeeper
* @TIMEKEEPER_AUX_LAST: The last AUX timekeeper
* @TIMEKEEPERS_MAX: The maximum number of timekeepers managed
*/
enum timekeeper_ids {
TIMEKEEPER_CORE,
#ifdef CONFIG_POSIX_AUX_CLOCKS
TIMEKEEPER_AUX_FIRST,
TIMEKEEPER_AUX_LAST = TIMEKEEPER_AUX_FIRST + MAX_AUX_CLOCKS - 1,
#endif
TIMEKEEPERS_MAX,
};

11
include/uapi/linux/time.h
View File

@ -64,6 +64,17 @@ struct timezone {
#define CLOCK_TAI 11
#define MAX_CLOCKS 16
/*
* AUX clock support. AUXiliary clocks are dynamically configured by
* enabling a clock ID. These clock can be steered independently of the
* core timekeeper. The kernel can support up to 8 auxiliary clocks, but
* the actual limit depends on eventual architecture constraints vs. VDSO.
*/
#define CLOCK_AUX MAX_CLOCKS
#define MAX_AUX_CLOCKS 8
#define CLOCK_AUX_LAST (CLOCK_AUX + MAX_AUX_CLOCKS - 1)
#define CLOCKS_MASK (CLOCK_REALTIME | CLOCK_MONOTONIC)
#define CLOCKS_MONO CLOCK_MONOTONIC

15
kernel/time/Kconfig
View File

@ -82,9 +82,9 @@ config CONTEXT_TRACKING_IDLE
help
Tracks idle state on behalf of RCU.
if GENERIC_CLOCKEVENTS
menu "Timers subsystem"
if GENERIC_CLOCKEVENTS
# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
# only related to the tick functionality. Oneshot clockevent devices
# are supported independent of this.
@ -208,6 +208,17 @@ config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
interval and NTP's maximum frequency drift of 500 parts
per million. If the clocksource is good enough for NTP,
it is good enough for the clocksource watchdog!
endif
config POSIX_AUX_CLOCKS
bool "Enable auxiliary POSIX clocks"
depends on POSIX_TIMERS
help
Auxiliary POSIX clocks are clocks which can be steered
independently of the core timekeeper, which controls the
MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to
provide e.g. lockless time accessors to independent PTP clocks
and other clock domains, which are not correlated to the TAI/NTP
notion of time.
endmenu
endif