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.
>
> [ ... ]
>
> 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@xxxxxxxxxx/
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"
>
