Re: [RFC PATCH bpf-next] bpf: Introduce bpf_timer

Alexei Starovoitov [off-list ref] writes:

On Sun, May 23, 2021 at 4:48 AM Toke Høiland-Jørgensen [off-list ref] wrote:

quoted

Still wrapping my head around this, but one thing immediately sprang to
mind:

quoted

+ * 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.

Okay, so this is really:

long bpf_timer_mod(struct bpf_timer *timer, u64 interval)

where 'interval' will be expressed in either milliseconds or nanoseconds
depending on which flags are passed to bpf_timer_init()? That's fine by
me, then; I just wanted to make sure that that 'msecs' was not an
indication that this was the only granularity these timers would
support... :)

-Toke