netdev - Re: [PATCH v2 net-next 2/6] net: add add indirect call wrapper in skb_release_head

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Message-ID: <9539f480-380b-4a29-afc5-025c3bf0973d@intel.com>
Date: Wed, 15 Oct 2025 14:54:13 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
	<xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, Kuniyuki Iwashima
	<kuniyu@...gle.com>, Willem de Bruijn <willemb@...gle.com>,
	<netdev@...r.kernel.org>, <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net-next 2/6] net: add add indirect call wrapper in
 skb_release_head_state()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 15 Oct 2025 05:46:27 -0700

> On Wed, Oct 15, 2025 at 5:30 AM Alexander Lobakin
> <aleksander.lobakin@...el.com> wrote:
>>
>> From: Eric Dumazet <edumazet@...gle.com>
>> Date: Wed, 15 Oct 2025 05:16:05 -0700
>>
>>> On Wed, Oct 15, 2025 at 5:02 AM Alexander Lobakin
>>> <aleksander.lobakin@...el.com> wrote:
>>>>
>>>> From: Eric Dumazet <edumazet@...gle.com>
>>>> Date: Tue, 14 Oct 2025 17:19:03 +0000
>>>>
>>>>> While stress testing UDP senders on a host with expensive indirect
>>>>> calls, I found cpus processing TX completions where showing
>>>>> a very high cost (20%) in sock_wfree() due to
>>>>> CONFIG_MITIGATION_RETPOLINE=y.
>>>>>
>>>>> Take care of TCP and UDP TX destructors and use INDIRECT_CALL_3() macro.
>>>>>
>>>>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>>>> ---
>>>>>  net/core/skbuff.c | 11 ++++++++++-
>>>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>>>> index bc12790017b0..692e3a70e75e 100644
>>>>> --- a/net/core/skbuff.c
>>>>> +++ b/net/core/skbuff.c
>>>>> @@ -1136,7 +1136,16 @@ void skb_release_head_state(struct sk_buff *skb)
>>>>>       skb_dst_drop(skb);
>>>>>       if (skb->destructor) {
>>>>>               DEBUG_NET_WARN_ON_ONCE(in_hardirq());
>>>>> -             skb->destructor(skb);
>>>>> +#ifdef CONFIG_INET
>>>>> +             INDIRECT_CALL_3(skb->destructor,
>>>>> +                             tcp_wfree, __sock_wfree, sock_wfree,
>>>>> +                             skb);
>>>>> +#else
>>>>> +             INDIRECT_CALL_1(skb->destructor,
>>>>> +                             sock_wfree,
>>>>> +                             skb);
>>>>> +
>>>>> +#endif
>>>>
>>>> Is it just me or seems like you ignored the suggestion/discussion under
>>>> v1 of this patch...
>>>>
>>>
>>> I did not. Please send a patch when you can demonstrate the difference.
>>
>> You "did not", but you didn't reply there, only sent v2 w/o any mention.
>>
>>>
>>> We are not going to add all the possible destructors unless there is evidence.
>>
>> There are numbers in the original discussion, you'd have noticed if you
>> did read.
>>
>> We only ask to add one more destructor which will help certain
>> perf-critical workloads. Add it to the end of the list, so that it won't
>> hurt your optimization.
>>
>> "Send a patch" means you're now changing these lines now and then they
>> would be changed once again, why...
> 
> I can not test what you propose.

You asked *me* to show the difference, in the orig discussion there's a
patch, there are tests and there is difference... :D

> 
> I can drop this patch instead, and keep it in Google kernels, (we had
> TCP support for years)

Ok, enough, leave this one as it is, we'll send the XSk bit ourselves.

> 
> Or... you can send a patch on top of it later.

Re "my Signed-off-by means I have strong confidence" -- sometimes we
also have Tested-by from other folks and it's never been a problem,
hey we're the community.

Thanks,
Olek