netdev - Re: [PATCH bpf-next] bpf: add sock_ops callbacks for data send/recv/acked events

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Message-ID: <1bcd4871-7403-41d9-8ae6-4df4878d9275@linux.alibaba.com>
Date: Wed, 29 Nov 2023 18:05:29 +0800
From: Philo Lu <lulie@...ux.alibaba.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: xuanzhuo@...ux.alibaba.com, dust.li@...ux.alibaba.com,
 alibuda@...ux.alibaba.com, guwen@...ux.alibaba.com,
 hengqi@...ux.alibaba.com, edumazet@...gle.com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net,
 andrii@...nel.org, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
 haoluo@...gle.com, jolsa@...nel.org, dsahern@...nel.org,
 netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: add sock_ops callbacks for data
 send/recv/acked events


On 2023/11/29 08:33, Martin KaFai Lau wrote:
> On 11/23/23 4:37 AM, Philo Lu wrote:
>> Sorry, I forgot to cc the maintainers.
>>
>> On 2023/11/23 11:07, Philo Lu wrote:
>>> Add 3 sock_ops operators, namely BPF_SOCK_OPS_DATA_SEND_CB,
>>> BPF_SOCK_OPS_DATA_RECV_CB, and BPF_SOCK_OPS_DATA_ACKED_CB. A flag
>>> BPF_SOCK_OPS_DATA_EVENT_CB_FLAG is provided to minimize the performance
>>> impact. The flag must be explicitly set to enable these callbacks.
>>>
>>> If the flag is enabled, bpf sock_ops program will be called every 
>>> time a
>>> tcp data packet is sent, received, and acked.
>>> BPF_SOCK_OPS_DATA_SEND_CB: call bpf after a data packet is sent.
>>> BPF_SOCK_OPS_DATA_RECV_CB: call bpf after a data packet is receviced.
>>> BPF_SOCK_OPS_DATA_ACKED_CB: call bpf after a valid ack packet is
>>> processed (some sent data are ackknowledged).
>>>
>>> We use these callbacks for fine-grained tcp monitoring, which collects
>>> and analyses every tcp request/response event information. The whole
>>> system has been described in SIGMOD'18 (see
>>> https://dl.acm.org/doi/pdf/10.1145/3183713.3190659 for details). To
>>> achieve this with bpf, we require hooks for data events that call
>>> sock_ops bpf (1) when any data packet is sent/received/acked, and (2)
>>> after critical tcp state variables have been updated (e.g., snd_una,
>>> snd_nxt, rcv_nxt). However, existing sock_ops operators cannot meet our
>>> requirements.
>>>
>>> Besides, these hooks also help to debug tcp when data send/recv/acked.
>
> This all sounds like a tracing use case. Why tracepoint is not used 
> instead?

Yes, our use case is pure tracing. We add hooks to sockops because we 
also use
other ops like BPF_SOCK_OPS_STATE_CB. Thus, sockops seems a natural solution
for us.

We can also use tracepoint (with sockops) instead. So we think which to use
depends on your opinions. Many thanks.