Re: [net-next v1] bpf: add bpf_ktime_get_real_ns helper

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xiangxia.m.yue@xxxxxxxxx writes:

> From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
>
> This patch introduce a new bpf_ktime_get_real_ns helper, which may
> help us to measure the skb latency in the ingress/forwarding path:
>
> HW/SW[1] -> ip_rcv/tcp_rcv_established -> tcp_recvmsg_locked/tcp_update_recv_tstamps
>
> * Insert BPF kprobe into ip_rcv/tcp_rcv_established invoking this helper.
>   Then we can inspect how long time elapsed since HW/SW.
> * If inserting BPF kprobe tcp_update_recv_tstamps invoked by tcp_recvmsg,
>   we can measure how much latency skb in tcp receive queue. The reason for
>   this can be application fetch the TCP messages too late.

Why not just use one of the existing ktime helpers and also add a BPF
probe to set the initial timestamp instead of relying on skb->tstamp?

-Toke



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