Commit f71f8530 authored by Tero Kristo's avatar Tero Kristo Committed by Alexei Starovoitov
Browse files

bpf: Add support for absolute value BPF timers 



Add a new flag BPF_F_TIMER_ABS that can be passed to bpf_timer_start()
to start an absolute value timer instead of the default relative value.
This makes the timer expire at an exact point in time, instead of a time
with latencies induced by both the BPF and timer subsystems.

Suggested-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: default avatarTero Kristo <tero.kristo@linux.intel.com>
Link: https://lore.kernel.org/r/20230302114614.2985072-2-tero.kristo@linux.intel.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent ec97a76f

include/uapi/linux/bpf.h

+15 −0
Original line number Diff line number Diff line
@@ -4969,6 +4969,12 @@ union bpf_attr { 
 *		different maps if key/value layout matches across maps.

 *		Every bpf_timer_set_callback() can have different callback_fn.

 *

 *		*flags* can be one of:

 *

 *		**BPF_F_TIMER_ABS**

 *			Start the timer in absolute expire value instead of the

 *			default relative one.

 *

 *	Return

 *		0 on success.

 *		**-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier
@@ -7097,4 +7103,13 @@ struct bpf_core_relo { 
	enum bpf_core_relo_kind kind;

};



/*

 * Flags to control bpf_timer_start() behaviour.

 *     - BPF_F_TIMER_ABS: Timeout passed is absolute time, by default it is

 *       relative to current time.

 */

enum {

	BPF_F_TIMER_ABS = (1ULL << 0),

};



#endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/helpers.c

+9 −2
Original line number Diff line number Diff line
@@ -1264,10 +1264,11 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla 
{

	struct bpf_hrtimer *t;

	int ret = 0;

	enum hrtimer_mode mode;



	if (in_nmi())

		return -EOPNOTSUPP;

	if (flags)

	if (flags > BPF_F_TIMER_ABS)

		return -EINVAL;

	__bpf_spin_lock_irqsave(&timer->lock);

	t = timer->timer;
@@ -1275,7 +1276,13 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla 
		ret = -EINVAL;

		goto out;

	}

	hrtimer_start(&t->timer, ns_to_ktime(nsecs), HRTIMER_MODE_REL_SOFT);



	if (flags & BPF_F_TIMER_ABS)

		mode = HRTIMER_MODE_ABS_SOFT;

	else

		mode = HRTIMER_MODE_REL_SOFT;



	hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode);

out:

	__bpf_spin_unlock_irqrestore(&timer->lock);

	return ret;

tools/include/uapi/linux/bpf.h

+15 −0
Original line number Diff line number Diff line
@@ -4969,6 +4969,12 @@ union bpf_attr { 
 *		different maps if key/value layout matches across maps.

 *		Every bpf_timer_set_callback() can have different callback_fn.

 *

 *		*flags* can be one of:

 *

 *		**BPF_F_TIMER_ABS**

 *			Start the timer in absolute expire value instead of the

 *			default relative one.

 *

 *	Return

 *		0 on success.

 *		**-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier
@@ -7097,4 +7103,13 @@ struct bpf_core_relo { 
	enum bpf_core_relo_kind kind;

};



/*

 * Flags to control bpf_timer_start() behaviour.

 *     - BPF_F_TIMER_ABS: Timeout passed is absolute time, by default it is

 *       relative to current time.

 */

enum {

	BPF_F_TIMER_ABS = (1ULL << 0),

};



#endif /* _UAPI__LINUX_BPF_H__ */