Date: Wed, 20 Mar 2024 13:30:44 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>, kernel@...cinc.com,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andrew Halaney <ahalaney@...hat.com>,
 Martin KaFai Lau <martin.lau@...nel.org>, bpf <bpf@...r.kernel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit
 for userspace tstamp packets

On 3/19/24 11:22 PM, Abhishek Chauhan (ABC) wrote:
> 
> 
> On 3/18/2024 12:02 PM, Abhishek Chauhan (ABC) wrote:
>>
>>
>> On 3/14/2024 3:29 PM, Abhishek Chauhan (ABC) wrote:
>>>
>>>
>>> On 3/14/2024 2:48 PM, Martin KaFai Lau wrote:
>>>> On 3/14/24 1:53 PM, Abhishek Chauhan (ABC) wrote:
>>>>>>> The bpf_convert_tstamp_{read,write} and the helper bpf_skb_set_tstamp need to be
>>>>>>> changed to handle the new "user_delivery_time" bit anyway, e.g.
>>>>>>> bpf_skb_set_tstamp(BPF_SKB_TSTAMP_DELIVERY_MONO) needs to clear the
>>>>>>> "user_delivery_time" bit.
>>>>>>>
>>>>>>> I think the "struct inet_frag_queue" also needs a new "user_delivery_time"
>>>>>>> field. "mono_delivery_time" is already in there.
>>>>
>>>> [ ... ]
>>>>
>>
>> Martin, Do we really need to add user_delivery_time as part of inet_frag_queue struct? I was wondering why is this required since we are using tstamp_type:2 to
>> distinguish between timestamp anyway .
>>
>> Let me know what you think ?
>>
>>>> I would think the first step is to revert this patch. I don't think much of the current patch can be reused.
>>>>
>>>>> 1. I will raise one patch to introduce rename mono_delivery_time to
>>>>> tstamp_type
>>>>
>>>> Right, I expect something like this:
>>>>
>>>> struct sk_buff {
>>>>          /* ... */
>>>> -            __u8                    mono_delivery_time:1;
>>>> +        __u8            tstamp_type:1;
>>>>          /* ... */
>>>> };
>>>>
>>>
>>> Okay ,This should be straight-forward.
>>>
>>>>> 2. I will introduce setting of userspace timestamp type as the second bit
>>>>> whem transmit_time is set.
>>>>
>>>> I expect the second patch should be introducing the enum first
>>>>
>>>> enum skb_tstamp_type {
>>>>      SKB_TSTAMP_TYPE_RX_REAL = 0, /* A RX (receive) time in real */
>>>>      SKB_TSTAMP_TYPE_TX_MONO = 1, /* A TX (delivery) time in mono */
>>>> };
>>>>
>>>> and start doing "skb->tstamp_type = SKB_TSTAMP_TYPE_TX_MONO;" instead of
>>>> "skb->tstamp_type = 1;"
>>>>
>>>> and the same for "skb->tstamp_type = SKB_TSTAMP_TYPE_RX_REAL;" instead of
>>>> "skb->tstamp_type = 0;"
>>>>
>>>>
>>>> This one I am not sure but probably need to change the skb_set_delivery_time() function signature also:
>>>>
>>>> static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
>>>> -                                        bool mono)
>>>> +                     enum skb_tstamp_type tstamp_type)
>>>>
>>> This should be straight-forward as well
>>>
>>>> The third patch is to change tstamp_type from 1 bit to 2 bits and add SKB_TSTAMP_TYPE_TX_USER.
>>>>
>>>> struct sk_buff {
>>>>          /* ... */
>>>> -        __u8            tstamp_type:1;
>>>> +        __u8            tstamp_type:2;
>>>>          /* ... */
>>>> };
>>>>
>>>> enum skb_tstamp_type {
>>>>      SKB_TSTAMP_TYPE_RX_REAL = 0,    /* A RX (receive) time in real */
>>>>      SKB_TSTAMP_TYPE_TX_MONO = 1,    /* A TX (delivery) time in mono */
>>>> +    SKB_TSTAMP_TYPE_TX_USER = 2,    /* A TX (delivery) time and its clock
>>>>                       * is in skb->sk->sk_clockid.
>>>>                       */
>>>>                 
>>>> };
>>>>
>>>> This will shift a bit out of the byte where tstamp_type lives. It should be the "inner_protocol_type" bit by my hand count. Please check if it is directly used in bpf instruction (filter.c). As far as I look, it is not, so should be fine. Some details about bpf instruction accessible skb bit field here: https://lore.kernel.org/all/20230321014115.997841-1-kuba@kernel.org/
>>> This is where i would need thorough reviews from you and Willem as my area of expertise is limited to part of network stack and BPF is not one of them.
>>> But i have plan on this and i know how to do it.
>>>
>>> Expect patches to be arriving to your inboxes next week, as we have a long weekend in Qualcomm
>>> Fingers crossed :)
>>>
>>>>
>>>>
>>>>> 3. This will be a first step to make the design scalable.
>>>>> 4. Tomorrow if we have more timestamp to support, upstream community has to do is
>>>>> update the enum and increase the bitfield from 2=>3 and so on.
>>>>>
>>>>> I need help from Martin to test the patch which renames the mono_delivery_time
>>>>> to tstamp_type (Which i feel should be straight forward as the value of the bit is 1)
>>>>
>>>> The bpf change is not a no-op rename of mono_delivery_time. It needs to take care of the new bit added to the tstamp_type. Please see the previous email (and I also left it in the beginning of this email).
>>>>
>>>> Thus, you need to compile the selftests/bpf/ and run it to verify the changes when handling the new bit. The Documentation/bpf/bpf_devel_QA.rst has the howto details. You probably only need the newer llvm (newer gcc should work also as bpf CI has been using it) and the newer pahole. I can definitely help if there is issue in running the test_progs in selftests/bpf or you have question on making the changes in filter.c. To run the test: "./test_progs -t tc_redirect/tc_redirect_dtime"
>>>>
> 
> Martin,
> I was able to compile test_progs and execute the above command mentioned by you . Does the output look okay for you ?
> 
> [ 3076.040766] IPv6: ADDRCONF(NETDEV_CHANGE): veth_src_fwd: link becomes ready
> [ 3076.040809] IPv6: ADDRCONF(NETDEV_CHANGE): veth_src: link becomes ready
> [ 3076.072844] IPv6: ADDRCONF(NETDEV_CHANGE): veth_dst: link becomes ready
> [ 3076.072880] IPv6: ADDRCONF(NETDEV_CHANGE): veth_dst_fwd: link becomes ready
> #214/5   tc_redirect/tc_redirect_dtime:OK
> #214     tc_redirect:OK

lgtm. thanks.

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