On Feb 23 2024, Eduard Zingerman wrote:
On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:
[...]
@@ -1282,7 +1333,7 @@ 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 | BPF_F_TIMER_CPU_PIN))
- if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN | BPF_F_TIMER_SLEEPABLE)) return -EINVAL; __bpf_spin_lock_irqsave(&timer->lock); t = timer->timer;
@@ -1299,7 +1350,10 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla if (flags & BPF_F_TIMER_CPU_PIN) mode |= HRTIMER_MODE_PINNED;
- hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode);
- if (flags & BPF_F_TIMER_SLEEPABLE)
schedule_work(&t->work);- else
hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode);It looks like nsecs is simply ignored for sleepable timers. Should this be hrtimer_start() that waits nsecs and schedules work, or schedule_delayed_work()? (but it takes delay in jiffies, which is probably too coarse). Sorry if I miss something.
Yeah, I agree it's confusing, but as mentioned by Toke in his reply, we should return -EINVAL if a timer value is provided (for now).
Alexei mentioned[0] that he didn't want to mix delays in hrtimers with workqueue as they are non deterministic. So AFAIU, I should add the only guarantee we can provide: a sleepable context, and proper delays in sleepable contexts will be added once we have a better workqueue selection available.
Cheers, Benjamin
[0] https://lore.kernel.org/bpf/CAO-hwJKz+eRA+BFLANTrEqz2jQAOANTE3c7eqNJ6wDqJR7j...