From: Martin KaFai Lau <martin.lau@linux.dev>
To: Abhishek Chauhan <quic_abchauha@quicinc.com>,
Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: kernel@quicinc.com, "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Andrew Halaney <ahalaney@redhat.com>,
Martin KaFai Lau <martin.lau@kernel.org>,
bpf <bpf@vger.kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit for userspace tstamp packets
Date: Tue, 12 Mar 2024 16:52:58 -0700 [thread overview]
Message-ID: <2a4cb416-5d95-459d-8c1c-3fb225240363@linux.dev> (raw)
In-Reply-To: <20240301201348.2815102-1-quic_abchauha@quicinc.com>
On 3/1/24 12:13 PM, Abhishek Chauhan wrote:
> Bridge driver today has no support to forward the userspace timestamp
> packets and ends up resetting the timestamp. ETF qdisc checks the
> packet coming from userspace and encounters to be 0 thereby dropping
> time sensitive packets. These changes will allow userspace timestamps
> packets to be forwarded from the bridge to NIC drivers.
>
> Setting the same bit (mono_delivery_time) to avoid dropping of
> userspace tstamp packets in the forwarding path.
>
> Existing functionality of mono_delivery_time remains unaltered here,
> instead just extended with userspace tstamp support for bridge
> forwarding path.
The patch currently broke the bpf selftest test_tc_dtime:
https://github.com/kernel-patches/bpf/actions/runs/8242487344/job/22541746675
In particular, there is a uapi field __sk_buff->tstamp_type which currently has
BPF_SKB_TSTAMP_DELIVERY_MONO to mean skb->tstamp has the MONO "delivery" time.
BPF_SKB_TSTAMP_UNSPEC means everything else (this could be a rx timestamp at
ingress or a delivery time set by user space).
__sk_buff->tstamp_type depends on skb->mono_delivery_time which does not
necessarily mean mono after this patch. I thought about fixing it on the bpf
side such that reading __sk_buff->tstamp_type only returns
BPF_SKB_TSTAMP_DELIVERY_MONO when the skb->mono_delivery_time is set and skb->sk
is IPPROTO_TCP. However, it won't work because of bpf_skb_set_tstamp().
There is a bpf helper, bpf_skb_set_tstamp(skb, tstamp,
BPF_SKB_TSTAMP_DELIVERY_MONO). This helper changes both the skb->tstamp and the
skb->mono_delivery_time. The expectation is this could change skb->tstamp in the
ingress skb and redirect to egress sch_fq. It could also set a mono time to
skb->tstamp where the udp sk->sk_clockid may not be necessary in mono and then
bpf_redirect to egress sch_fq. When bpf_skb_set_tstamp(skb, tstamp,
BPF_SKB_TSTAMP_DELIVERY_MONO) succeeds, reading __sk_buff->tstamp_type expects
BPF_SKB_TSTAMP_DELIVERY_MONO also.
I ran out of idea to solve this uapi breakage.
I am afraid it may need to go back to v1 idea and use another bit
(user_delivery_time) in the skb.
next prev parent reply other threads:[~2024-03-12 23:53 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 20:13 [PATCH net-next v4] net: Re-use and set mono_delivery_time bit for userspace tstamp packets Abhishek Chauhan
2024-03-01 22:21 ` Willem de Bruijn
2024-03-05 13:00 ` patchwork-bot+netdevbpf
2024-03-12 23:52 ` Martin KaFai Lau [this message]
2024-03-13 4:34 ` Abhishek Chauhan (ABC)
2024-03-13 5:32 ` Abhishek Chauhan (ABC)
2024-03-13 8:52 ` Willem de Bruijn
2024-03-13 18:42 ` Martin KaFai Lau
2024-03-13 19:36 ` Willem de Bruijn
2024-03-13 20:59 ` Abhishek Chauhan (ABC)
2024-03-13 21:19 ` Martin KaFai Lau
2024-03-13 21:41 ` Daniel Borkmann
2024-03-13 21:01 ` Martin KaFai Lau
2024-03-13 21:26 ` Abhishek Chauhan (ABC)
2024-03-13 21:40 ` Willem de Bruijn
2024-03-13 22:08 ` Martin KaFai Lau
2024-03-14 9:49 ` Willem de Bruijn
2024-03-14 19:21 ` Martin KaFai Lau
2024-03-14 20:28 ` Willem de Bruijn
2024-03-14 20:53 ` Abhishek Chauhan (ABC)
2024-03-14 21:48 ` Martin KaFai Lau
2024-03-14 21:54 ` Martin KaFai Lau
2024-03-14 22:29 ` Abhishek Chauhan (ABC)
2024-03-18 19:02 ` Abhishek Chauhan (ABC)
2024-03-19 19:46 ` Martin KaFai Lau
2024-03-19 20:12 ` Abhishek Chauhan (ABC)
2024-03-20 6:22 ` Abhishek Chauhan (ABC)
2024-03-20 20:30 ` Martin KaFai Lau
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