netdev - Re: [PATCH] net: Add tcp_drop

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Message-ID: <CALOAHbDk48363Bs3OyXVw-PpTLc08-+MEo4bq9kXq1EWtyh24g@mail.gmail.com>
Date: Wed, 23 Oct 2024 22:34:27 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, 
	pabeni@...hat.com, rostedt@...dmis.org, mhiramat@...nel.org, 
	mathieu.desnoyers@...icios.com, netdev@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, Menglong Dong <menglong8.dong@...il.com>
Subject: Re: [PATCH] net: Add tcp_drop_reason tracepoint

On Wed, Oct 23, 2024 at 9:01 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Oct 23, 2024 at 2:33 PM Yafang Shao <laoar.shao@...il.com> wrote:
> >
> > 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 introduce a dedicated tracepoint
> > for monitoring.
>
> This patch would require changes in user space tracers.
> I am surprised no one came up with a noinline variant.
>
> __bpf_kfunc is using
>
> #define __bpf_kfunc __used __retain noinline
>
> I would rather not have include/trace/events/tcp.h becoming the
> biggest file in TCP stack...

I’d prefer not to introduce a new tracepoint if we can easily hook it
with BPF. Does the following change look good to you?

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 092456b8f8af..ebea844cc974 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4720,7 +4720,7 @@ static bool tcp_ooo_try_coalesce(struct sock *sk,
        return res;
 }

-static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
+noinline static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
                            enum skb_drop_reason reason)
 {
        sk_drops_add(sk, skb);




--
Regards
Yafang