Commit d6247ecb authored by David Vernet's avatar David Vernet Committed by Daniel Borkmann
Browse files

bpf: Add ability to pin bpf timer to calling CPU 



BPF supports creating high resolution timers using bpf_timer_* helper
functions. Currently, only the BPF_F_TIMER_ABS flag is supported, which
specifies that the timeout should be interpreted as absolute time. It
would also be useful to be able to pin that timer to a core. For
example, if you wanted to make a subset of cores run without timer
interrupts, and only have the timer be invoked on a single core.

This patch adds support for this with a new BPF_F_TIMER_CPU_PIN flag.
When specified, the HRTIMER_MODE_PINNED flag is passed to
hrtimer_start(). A subsequent patch will update selftests to validate.

Signed-off-by: default avatarDavid Vernet <void@manifault.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSong Liu <song@kernel.org>
Acked-by: default avatarHou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20231004162339.200702-2-void@manifault.com
parent 84cb9cbd

include/uapi/linux/bpf.h

+4 −0
Original line number Diff line number Diff line
@@ -5096,6 +5096,8 @@ union bpf_attr { 
 *		**BPF_F_TIMER_ABS**

 *			Start the timer in absolute expire value instead of the

 *			default relative one.

 *		**BPF_F_TIMER_CPU_PIN**

 *			Timer will be pinned to the CPU of the caller.

 *

 *	Return

 *		0 on success.
@@ -7309,9 +7311,11 @@ struct bpf_core_relo { 
 * Flags to control bpf_timer_start() behaviour.

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

 *       relative to current time.

 *     - BPF_F_TIMER_CPU_PIN: Timer will be pinned to the CPU of the caller.

 */

enum {

	BPF_F_TIMER_ABS = (1ULL << 0),

	BPF_F_TIMER_CPU_PIN = (1ULL << 1),

};



/* BPF numbers iterator state */

kernel/bpf/helpers.c

+4 −1
Original line number Diff line number Diff line
@@ -1272,7 +1272,7 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla 


	if (in_nmi())

		return -EOPNOTSUPP;

	if (flags > BPF_F_TIMER_ABS)

	if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN))

		return -EINVAL;

	__bpf_spin_lock_irqsave(&timer->lock);

	t = timer->timer;
@@ -1286,6 +1286,9 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla 
	else

		mode = HRTIMER_MODE_REL_SOFT;



	if (flags & BPF_F_TIMER_CPU_PIN)

		mode |= HRTIMER_MODE_PINNED;



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

out:

	__bpf_spin_unlock_irqrestore(&timer->lock);

tools/include/uapi/linux/bpf.h

+4 −0
Original line number Diff line number Diff line
@@ -5096,6 +5096,8 @@ union bpf_attr { 
 *		**BPF_F_TIMER_ABS**

 *			Start the timer in absolute expire value instead of the

 *			default relative one.

 *		**BPF_F_TIMER_CPU_PIN**

 *			Timer will be pinned to the CPU of the caller.

 *

 *	Return

 *		0 on success.
@@ -7309,9 +7311,11 @@ struct bpf_core_relo { 
 * Flags to control bpf_timer_start() behaviour.

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

 *       relative to current time.

 *     - BPF_F_TIMER_CPU_PIN: Timer will be pinned to the CPU of the caller.

 */

enum {

	BPF_F_TIMER_ABS = (1ULL << 0),

	BPF_F_TIMER_CPU_PIN = (1ULL << 1),

};



/* BPF numbers iterator state */