netdev - Re: [PATCH v5 1/5] net-timestamp: COMPLETION timestamp on packet tx completion

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Message-ID: <6cf69a7e-da5d-49da-ab05-4523f2914254@molgen.mpg.de>
Date: Wed, 19 Mar 2025 16:48:26 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Pauli Virtanen <pav@....fi>
Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>,
 linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
 davem@...emloft.net, kuba@...nel.org, willemdebruijn.kernel@...il.com
Subject: Re: [PATCH v5 1/5] net-timestamp: COMPLETION timestamp on packet tx
 completion

Dear Pauli,


Thank you for your patch. Two minor comments, should you resend.

You could make the summary/title a statement:

Add COMPLETION timestamp on packet tx completion

Am 18.03.25 um 20:06 schrieb Pauli Virtanen:
> Add SOF_TIMESTAMPING_TX_COMPLETION, for requesting a software timestamp
> when hardware reports a packet completed.
> 
> Completion tstamp is useful for Bluetooth, as hardware timestamps do not
> exist in the HCI specification except for ISO packets, and the hardware
> has a queue where packets may wait.  In this case the software SND
> timestamp only reflects the kernel-side part of the total latency
> (usually small) and queue length (usually 0 unless HW buffers
> congested), whereas the completion report time is more informative of
> the true latency.
> 
> It may also be useful in other cases where HW TX timestamps cannot be
> obtained and user wants to estimate an upper bound to when the TX
> probably happened.
> 
> Signed-off-by: Pauli Virtanen <pav@....fi>
> ---
> 
> Notes:
>      v5:
>      - back to decoupled COMPLETION & SND, like in v3
>      - BPF reporting not implemented here
> 
>   Documentation/networking/timestamping.rst | 8 ++++++++
>   include/linux/skbuff.h                    | 7 ++++---
>   include/uapi/linux/errqueue.h             | 1 +
>   include/uapi/linux/net_tstamp.h           | 6 ++++--
>   net/core/skbuff.c                         | 2 ++
>   net/ethtool/common.c                      | 1 +
>   net/socket.c                              | 3 +++
>   7 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
> index 61ef9da10e28..b8fef8101176 100644
> --- a/Documentation/networking/timestamping.rst
> +++ b/Documentation/networking/timestamping.rst
> @@ -140,6 +140,14 @@ SOF_TIMESTAMPING_TX_ACK:
>     cumulative acknowledgment. The mechanism ignores SACK and FACK.
>     This flag can be enabled via both socket options and control messages.
>   
> +SOF_TIMESTAMPING_TX_COMPLETION:
> +  Request tx timestamps on packet tx completion.  The completion
> +  timestamp is generated by the kernel when it receives packet a
> +  completion report from the hardware. Hardware may report multiple

… receives packate a completion … sounds strange to me, but I am a 
non-native speaker.

[…]


Kind regards,

Paul