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

On Mon, May 24, 2021 at 9:59 PM Cong Wang [off-list ref] wrote:

On Mon, May 24, 2021 at 8:16 PM Cong Wang [off-list ref] wrote:

quoted

On Sun, May 23, 2021 at 9:01 AM Alexei Starovoitov
[off-list ref] wrote:

quoted

On Fri, May 21, 2021 at 2:37 PM Cong Wang [off-list ref] wrote:

quoted

Hi, Alexei

On Thu, May 20, 2021 at 11:52 PM Alexei Starovoitov
[off-list ref] wrote:

quoted

Introduce 'struct bpf_timer' that can be embedded in most BPF map types
and helpers to operate on it:
long bpf_timer_init(struct bpf_timer *timer, void *callback, int flags)
long bpf_timer_mod(struct bpf_timer *timer, u64 msecs)
long bpf_timer_del(struct bpf_timer *timer)

Like we discussed, this approach would make the timer harder
to be independent of other eBPF programs, which is a must-have
for both of our use cases (mine and Jamal's). Like you explained,
this requires at least another program array, a tail call, a mandatory
prog pinning to work.

That is simply not true.

Which part is not true? The above is what I got from your explanation.

I tried to write some code sketches to use your timer to implement
our conntrack logic, below shows how difficult it is to use,

Was it difficult because you've used tail_call and over complicated
the progs for no good reason?

SEC("ingress")
void ingress(struct __sk_buff *skb)
{
        struct tuple tuple;
        // extract tuple from skb

        if (bpf_map_lookup_elem(&timers, &key) == NULL)
                bpf_tail_call(NULL, &jmp_table, 0);
                // here is not reachable unless failure
        val = bpf_map_lookup_elem(&conntrack, &tuple);
        if (val && val->expires < now) {
                bpf_tail_call(NULL, &jmp_table, 1);
                // here is not reachable unless failure
        }
}

SEC("egress")
void egress(struct __sk_buff *skb)
{
        struct tuple tuple;
        // extract tuple from skb

        if (bpf_map_lookup_elem(&timers, &key) == NULL)
                bpf_tail_call(NULL, &jmp_table, 0);
                // here is not reachable unless failure
        val = bpf_map_lookup_elem(&conntrack, &tuple);
        if (val && val->expires < now) {
                bpf_tail_call(NULL, &jmp_table, 1);
                // here is not reachable unless failure

tail_calls are unnecessary. Just call the funcs directly.
All lookups and maps are unnecessary as well.
Looks like a single global timer will be enough for this use case.

In general the garbage collection in any form doesn't scale.
The conntrack logic doesn't need it. The cillium conntrack is a great
example of how to implement a conntrack without GC.