Re: [PATCH v6 net-next 0/13] Preserve mono delivery time (EDT) in skb->tstamp

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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 !



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