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

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Message-ID: <CABBYNZJk2QjUaJCurAocMAJdOTfFHCjKO_S2rcxWLwTv8K9VDw@mail.gmail.com>
Date: Thu, 20 Mar 2025 10:43:00 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: Pauli Virtanen <pav@....fi>, 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

Hi Pauli, Willem, Jason,

On Wed, Mar 19, 2025 at 11:48 AM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
>
> 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

Is v5 considered good enough to be merged into bluetooth-next and can
this be send to in this merge window or you think it is best to leave
for the next? In my opinion it could go in so we use the RC period to
stabilize it.

-- 
Luiz Augusto von Dentz