# Re: \[RFC PATCH bpf-next\] bpf: Introduce bpf\_timer

- From: Alexei Starovoitov \<hidden\>
- Date: 2021-05-24 17:34:11 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/05/7769468
- Thread: https://ratatoskr.run/netdev/2021/05/7769404/t.md

```text
On Sun, May 23, 2021 at 8:58 AM Alexei Starovoitov
[ref] wrote:
>
> On Sun, May 23, 2021 at 4:48 AM Toke Høiland-Jørgensen [ref] wrote:
> >
> > Still wrapping my head around this, but one thing immediately sprang to
> > mind:
> >
> > > + * long bpf_timer_mod(struct bpf_timer *timer, u64 msecs)
> > > + *   Description
> > > + *           Set the timer expiration N msecs from the current time.
> > > + *   Return
> > > + *           zero
> >
> > Could we make this use nanoseconds (and wire it up to hrtimers) instead?
> > I would like to eventually be able to use this for pacing out network
> > packets, and msec precision is way too coarse for that...
>
> msecs are used to avoid exposing jiffies to bpf prog, since msec_to_jiffies
> isn't trivial to do in the bpf prog unlike the kernel.
> hrtimer would be great to support as well.
> It could be implemented via flags (which are currently zero only)
> but probably not as a full replacement for jiffies based timers.
> Like array vs hash. bpf_timer can support both.

After reading the hrtimer code I might take the above statement back...
hrtimer looks strictly better than timerwheel and jiffies.
It scales well and there are no concerns with overload,
since sys_nanonsleep and tcp are heavy users.
So I'm thinking to drop jiffies approach and do hrtimer only.
wdyt?
```