netdev - Re: [PATCH v2] tracepoint: add new `tcp:tcp_ca

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Date: Tue, 8 Aug 2023 16:46:41 +0800
From: Manjusaka <me@...jusaka.me>
To: Eric Dumazet <edumazet@...gle.com>
Cc: ncardwell@...gle.com, bpf@...r.kernel.org, davem@...emloft.net,
 dsahern@...nel.org, kuba@...nel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, mhiramat@...nel.org,
 netdev@...r.kernel.org, pabeni@...hat.com, rostedt@...dmis.org
Subject: Re: [PATCH v2] tracepoint: add new `tcp:tcp_ca_event` trace event



On 2023/8/8 16:26, Eric Dumazet wrote:
> On Tue, Aug 8, 2023 at 7:59 AM Manjusaka <me@...jusaka.me> wrote:
>>
>> In normal use case, the tcp_ca_event would be changed in high frequency.
>>
>> It's a good indicator to represent the network quanlity.
> 
> quality ?
> 
> Honestly, it is more about TCP stack tracing than 'network quality'
> 
>>
>> So I propose to add a `tcp:tcp_ca_event` trace event
>> like `tcp:tcp_cong_state_set` to help the people to
>> trace the TCP connection status
>>
>> Signed-off-by: Manjusaka <me@...jusaka.me>
>> ---
>>  include/net/tcp.h          |  9 ++------
>>  include/trace/events/tcp.h | 45 ++++++++++++++++++++++++++++++++++++++
>>  net/ipv4/tcp_cong.c        | 10 +++++++++
>>  3 files changed, 57 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/net/tcp.h b/include/net/tcp.h
>> index 0ca972ebd3dd..a68c5b61889c 100644
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -1154,13 +1154,8 @@ static inline bool tcp_ca_needs_ecn(const struct sock *sk)
>>         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
>>  }
>>
>> -static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
>> -{
>> -       const struct inet_connection_sock *icsk = inet_csk(sk);
>> -
>> -       if (icsk->icsk_ca_ops->cwnd_event)
>> -               icsk->icsk_ca_ops->cwnd_event(sk, event);
>> -}
>> +/* from tcp_cong.c */
>> +void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event);
>>
>>  /* From tcp_cong.c */
>>  void tcp_set_ca_state(struct sock *sk, const u8 ca_state);
>> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
>> index bf06db8d2046..b374eb636af9 100644
>> --- a/include/trace/events/tcp.h
>> +++ b/include/trace/events/tcp.h
>> @@ -416,6 +416,51 @@ TRACE_EVENT(tcp_cong_state_set,
>>                   __entry->cong_state)
>>  );
>>
>> +TRACE_EVENT(tcp_ca_event,
>> +
>> +       TP_PROTO(struct sock *sk, const u8 ca_event),
>> +
>> +       TP_ARGS(sk, ca_event),
>> +
>> +       TP_STRUCT__entry(
>> +               __field(const void *, skaddr)
>> +               __field(__u16, sport)
>> +               __field(__u16, dport)
>> +               __array(__u8, saddr, 4)
>> +               __array(__u8, daddr, 4)
>> +               __array(__u8, saddr_v6, 16)
>> +               __array(__u8, daddr_v6, 16)
>> +               __field(__u8, ca_event)
>> +       ),
>> +
> 
> Please add the family (look at commit 3dd344ea84e1 ("net: tracepoint:
> exposing sk_family in all tcp:tracepoints"))
> 
> 
> 
>> +       TP_fast_assign(
>> +               struct inet_sock *inet = inet_sk(sk);
>> +               __be32 *p32;
>> +
>> +               __entry->skaddr = sk;
>> +
>> +               __entry->sport = ntohs(inet->inet_sport);
>> +               __entry->dport = ntohs(inet->inet_dport);
>> +
>> +               p32 = (__be32 *) __entry->saddr;
>> +               *p32 = inet->inet_saddr;
>> +
>> +               p32 = (__be32 *) __entry->daddr;
>> +               *p32 =  inet->inet_daddr;
> 
> We keep copying IPv4 addresses that might contain garbage for IPv6 sockets :/
> 
>> +
>> +               TP_STORE_ADDRS(__entry, inet->inet_saddr, inet->inet_daddr,
>> +                          sk->sk_v6_rcv_saddr, sk->sk_v6_daddr);
> 
> I will send a cleanup, because IP_STORE_ADDRS() should really take
> care of all details.
> 
> 
>> +
>> +               __entry->ca_event = ca_event;
>> +       ),
>> +
>> +       TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c ca_event=%u",
>> +                 __entry->sport, __entry->dport,
>> +                 __entry->saddr, __entry->daddr,
>> +                 __entry->saddr_v6, __entry->daddr_v6,
>> +                 __entry->ca_event)
> 
> Please print the symbol instead of numeric ca_event.
> 
> Look at show_tcp_state_name() for instance.

Thanks for the kindness code review, I still get some issue here(Sorry for the first time to contribute):

1. > We keep copying IPv4 addresses that might contain garbage for IPv6 sockets :/

I'm not getting your means, would you mean that we should only save the IPv4 Address here?

2. > I will send a cleanup, because IP_STORE_ADDRS() should really take care of all details.

I think you will make the address assignment code in TP_fast_assign as a new function. 

Should I submit the new change until you send the cleanup patch or I can make this in my patch(cleanup the address assignment)