netdev - Re: [PATCH v3 5/5] io_uring/netcmd: add tx timestamping cmd support

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Message-ID: <ae60dd48-9e21-4a9d-a8d8-d98a2e8e6c8f@kernel.dk>
Date: Thu, 12 Jun 2025 08:31:33 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemb@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Richard Cochran <richardcochran@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH v3 5/5] io_uring/netcmd: add tx timestamping cmd support

On 6/12/25 8:26 AM, Pavel Begunkov wrote:
>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
>>> index cfd17e382082..5c89e6f6d624 100644
>>> --- a/include/uapi/linux/io_uring.h
>>> +++ b/include/uapi/linux/io_uring.h
>>> @@ -968,6 +968,15 @@ enum io_uring_socket_op {
>>>       SOCKET_URING_OP_SIOCOUTQ,
>>>       SOCKET_URING_OP_GETSOCKOPT,
>>>       SOCKET_URING_OP_SETSOCKOPT,
>>> +    SOCKET_URING_OP_TX_TIMESTAMP,
>>> +};
>>> +
>>> +#define IORING_CQE_F_TIMESTAMP_HW    ((__u32)1 << IORING_CQE_BUFFER_SHIFT)
>>> +#define IORING_TIMESTAMP_TSTYPE_SHIFT    (IORING_CQE_BUFFER_SHIFT + 1)
>>
>> Don't completely follow this, would at the very least need a comment.
>> Whether it's a HW or SW timestamp is flagged in the upper 16 bits, just
>> like a provided buffer ID. But since we don't use buffer IDs here, then
>> it's up for grabs. Do we have other commands that use the upper flags
>> space for command private flags?
> 
> Probably not, but the place is better than the lower half, which
> has common flags like F_MORE, especially since the patch is already
> using it to store the type.

Just pondering whether it should be formalized, but probably no point as
each opcode should be free to use the space as it wants.

>> The above makes sense, but then what is IORING_TIMESTAMP_TSTYPE_SHIFT?
> 
> It's a shift for where the timestamp type is stored, HW vs SW is
> not a timestamp type. I don't get the question.

Please add a spec like comment on top of it explaining the usage of the
upper bits in the flags field, then. I try to keep the io_uring.h uapi
header pretty well commented and documented.

-- 
Jens Axboe