Received-SPF: pass (google.com: domain of linux-kernel+bounces-164716-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <30c91655-a1ba-44da-900b-f2a70ed9f961@quicinc.com>
Date: Tue, 30 Apr 2024 13:40:10 -0700
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support
 clockid_t timestamp type
Content-Language: en-US
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
        Martin KaFai Lau
	<martin.lau@linux.dev>
CC: "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet
	<edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni
	<pabeni@redhat.com>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Andrew Halaney <ahalaney@redhat.com>,
        "Martin
 KaFai Lau" <martin.lau@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
        <kernel@quicinc.com>
References: <20240424222028.1080134-1-quic_abchauha@quicinc.com>
 <20240424222028.1080134-3-quic_abchauha@quicinc.com>
 <2b2c3eb1-df87-40fe-b871-b52812c8ecd0@linux.dev>
 <e761e1de-0e11-4541-a4db-a1b793a60674@quicinc.com>
 <379558fe-a6e2-444b-a6a7-ef233efa8311@linux.dev>
 <6eb5b283-a9bd-4081-8bce-a60d72af430c@quicinc.com>
 <663153f92a297_33210f29423@willemb.c.googlers.com.notmuch>
From: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>
In-Reply-To: <663153f92a297_33210f29423@willemb.c.googlers.com.notmuch>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit


On 4/30/2024 1:26 PM, Willem de Bruijn wrote:
> Abhishek Chauhan (ABC) wrote:
>>
>>
>> On 4/26/2024 4:50 PM, Martin KaFai Lau wrote:
>>> On 4/26/24 11:46 AM, Abhishek Chauhan (ABC) wrote:
>>>>>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>>>>>> index 591226dcde26..f195b31d6e75 100644
>>>>>> --- a/net/ipv4/ip_output.c
>>>>>> +++ b/net/ipv4/ip_output.c
>>>>>> @@ -1457,7 +1457,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>>>>>>          skb->priority = (cork->tos != -1) ? cork->priority: READ_ONCE(sk->sk_priority);
>>>>>>        skb->mark = cork->mark;
>>>>>> -    skb->tstamp = cork->transmit_time;
>>>>>> +    skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
>>>>> hmm... I think this will break for tcp. This sequence in particular:
> 
> Good catch, thanks!
> 
>>>>>
>>>>> tcp_v4_timewait_ack()
>>>>>    tcp_v4_send_ack()
>>>>>      ip_send_unicast_reply()
>>>>>        ip_push_pending_frames()
>>>>>          ip_finish_skb()
>>>>>            __ip_make_skb()
>>>>>              /* sk_clockid is REAL but cork->transmit_time should be in mono */
>>>>>              skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);;
>>>>>
>>>>> I think I hit it from time to time when running the test in this patch set.
>>>>>
>>>> do you think i need to check for protocol type here . since tcp uses Mono and the rest according to the new design is based on
>>>> sk->sk_clockid
>>>> if (iph->protocol == IPPROTO_TCP)
>>>>     skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, CLOCK_MONOTONIC);
>>>> else
>>>>     skb_set_tstamp_type_frm_clkid(skb, cork->transmit_time, sk->sk_clockid);
>>>
>>> Looks ok. iph->protocol is from sk->sk_protocol. I would defer to Willem input here.
>>>
>>> There is at least one more place that needs this protocol check, __ip6_make_skb().
>>
>> Sounds good. I will wait for Willem to comment here. 
> 
> This would be sk_is_tcp(sk).
> 
> I think we want to avoid special casing if we can. Note the if.
> 
> If TCP always uses monotonic, we could consider initializing
> sk_clockid to CLOCK_MONONOTIC in tcp_init_sock.
> 
> I guess TCP logic currently entirely ignores sk_clockid. If we are to
> start using this, then setsocktop SO_TXTIME must explicitly fail or
> ignore for TCP sockets, or silently skip the write.
> 
> All of that is more complexity. Than is maybe warranted for this one
> case. So no objections from me to special casing using sk_is_tcp(sk)
> either.
> 
>

Thanks Willem and Martin for all the support and reviews. 
I will take care of this in the next RFC patch
- adding the sk_is_tcp check and setting tstamp_type to mono for tcp

> 
>