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bpf: Add ability to pin bpf timer to calling CPU

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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: David Vernet <void@manifault.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20231004162339.200702-2-void@manifault.com
This commit is contained in:
David Vernet 2023-10-04 11:23:38 -05:00 committed by Daniel Borkmann
parent 84cb9cbd91
commit d6247ecb6c
3 changed files with 12 additions and 1 deletions
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4
include/uapi/linux/bpf.h
View file

@ -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 */

5
kernel/bpf/helpers.c
View file

@ -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);

4
tools/include/uapi/linux/bpf.h
View file

@ -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 */