netdev - Re: [PATCH 2/2] net: tcp: Add noinline_for_tracing annotation for tcp_drop

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Message-Id: <b2e2b3e0-7190-43e5-963d-fc291bba6f81@app.fastmail.com>
Date: Thu, 24 Oct 2024 13:52:06 -0700
From: "Daniel Xu" <dxu@...uu.xyz>
To: "Kuniyuki Iwashima" <kuniyu@...zon.com>, laoar.shao@...il.com
Cc: "David Miller" <davem@...emloft.net>, dsahern@...nel.org,
 "Eric Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>,
 menglong8.dong@...il.com, netdev@...r.kernel.org,
 "Paolo Abeni" <pabeni@...hat.com>
Subject: Re: [PATCH 2/2] net: tcp: Add noinline_for_tracing annotation for
 tcp_drop_reason()

Hi Kuniyuki,

On Thu, Oct 24, 2024, at 12:13 PM, Kuniyuki Iwashima wrote:
> From: Yafang Shao <laoar.shao@...il.com>
> Date: Thu, 24 Oct 2024 17:37:42 +0800
>> We previously hooked the tcp_drop_reason() function using BPF to monitor
>> TCP drop reasons. However, after upgrading our compiler from GCC 9 to GCC
>> 11, tcp_drop_reason() is now inlined, preventing us from hooking into it.
>> To address this, it would be beneficial to make noinline explicitly for
>> tracing.
>> 
>> Link: https://lore.kernel.org/netdev/CANn89iJuShCmidCi_ZkYABtmscwbVjhuDta1MS5LxV_4H9tKOA@mail.gmail.com/
>> Suggested-by: Eric Dumazet <edumazet@...gle.com>
>> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
>> Cc: Menglong Dong <menglong8.dong@...il.com>
>
> I saw a somewhat related post yesterday.
> https://x.com/__dxu/status/1849271647989068107

Glad to hear you're interested!

>
> Daniel, could we apply your approach to this issue in the near future ?
>

I suppose that depends on how you define "near". I'm being vague
in that thread b/c we're still experimenting and have a couple things
to look at still. But eventually, hopefully yes. Perhaps some time
within a year if you had to press me.

> Thread link: 
> https://lore.kernel.org/netdev/20241024093742.87681-1-laoar.shao@gmail.com/
>
>
>> ---
>>  net/ipv4/tcp_input.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index cc05ec1faac8..cf1e2e3a7407 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -4894,8 +4894,8 @@ static bool tcp_ooo_try_coalesce(struct sock *sk,
>>  	return res;
>>  }
>>  
>> -static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
>> -			    enum skb_drop_reason reason)
>> +noinline_for_tracing static void
>> +tcp_drop_reason(struct sock *sk, struct sk_buff *skb, enum skb_drop_reason reason)
>>  {
>>  	sk_drops_add(sk, skb);
>>  	sk_skb_reason_drop(sk, skb, reason);
>> -- 
>> 2.43.5
>>