On Wed, Mar 2, 2022 at 11:55 AM Martin KaFai Lau <kafai@xxxxxx> wrote: > > skb->tstamp was first used as the (rcv) timestamp. > The major usage is to report it to the user (e.g. SO_TIMESTAMP). > > Later, skb->tstamp is also set as the (future) delivery_time (e.g. EDT in TCP) > during egress and used by the qdisc (e.g. sch_fq) to make decision on when > the skb can be passed to the dev. > > Currently, there is no way to tell skb->tstamp having the (rcv) timestamp > or the delivery_time, so it is always reset to 0 whenever forwarded > between egress and ingress. > > While it makes sense to always clear the (rcv) timestamp in skb->tstamp > to avoid confusing sch_fq that expects the delivery_time, it is a > performance issue [0] to clear the delivery_time if the skb finally > egress to a fq@phy-dev. > > This set is to keep the mono delivery time and make it available to > the final egress interface. Please see individual patch for > the details. > > [0] (slide 22): https://linuxplumbersconf.org/event/11/contributions/953/attachments/867/1658/LPC_2021_BPF_Datapath_Extensions.pdf > For the whole series Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx> Thanks !
