On Wed, Mar 19, 2025 at 3:08 AM Pauli Virtanen <pav@xxxxxx> wrote:
>
> 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@xxxxxx>
Hi Pauli,
This patch overall looks good to me but it depends on the small
question in another patch that is relevant to how we use this new flag
in reality. Let's discuss a bit there.
Thanks,
Jason
> ---
>
> 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
> + packets at once, and completion timestamps reflect the timing of the
> + report and not actual tx time. This flag can be enabled via both
> + socket options and control messages.
> +
>
> 1.3.2 Timestamp Reporting
> ^^^^^^^^^^^^^^^^^^^^^^^^^
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index cd8294cdc249..b974a277975a 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -478,8 +478,8 @@ enum {
> /* device driver is going to provide hardware time stamp */
> SKBTX_IN_PROGRESS = 1 << 2,
>
> - /* reserved */
> - SKBTX_RESERVED = 1 << 3,
> + /* generate software time stamp on packet tx completion */
> + SKBTX_COMPLETION_TSTAMP = 1 << 3,
>
> /* generate wifi status information (where possible) */
> SKBTX_WIFI_STATUS = 1 << 4,
> @@ -498,7 +498,8 @@ enum {
>
> #define SKBTX_ANY_SW_TSTAMP (SKBTX_SW_TSTAMP | \
> SKBTX_SCHED_TSTAMP | \
> - SKBTX_BPF)
> + SKBTX_BPF | \
> + SKBTX_COMPLETION_TSTAMP)
> #define SKBTX_ANY_TSTAMP (SKBTX_HW_TSTAMP | \
> SKBTX_ANY_SW_TSTAMP)
>
> diff --git a/include/uapi/linux/errqueue.h b/include/uapi/linux/errqueue.h
> index 3c70e8ac14b8..1ea47309d772 100644
> --- a/include/uapi/linux/errqueue.h
> +++ b/include/uapi/linux/errqueue.h
> @@ -73,6 +73,7 @@ enum {
> SCM_TSTAMP_SND, /* driver passed skb to NIC, or HW */
> SCM_TSTAMP_SCHED, /* data entered the packet scheduler */
> SCM_TSTAMP_ACK, /* data acknowledged by peer */
> + SCM_TSTAMP_COMPLETION, /* packet tx completion */
> };
>
> #endif /* _UAPI_LINUX_ERRQUEUE_H */
> diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
> index 55b0ab51096c..383213de612a 100644
> --- a/include/uapi/linux/net_tstamp.h
> +++ b/include/uapi/linux/net_tstamp.h
> @@ -44,8 +44,9 @@ enum {
> SOF_TIMESTAMPING_BIND_PHC = (1 << 15),
> SOF_TIMESTAMPING_OPT_ID_TCP = (1 << 16),
> SOF_TIMESTAMPING_OPT_RX_FILTER = (1 << 17),
> + SOF_TIMESTAMPING_TX_COMPLETION = (1 << 18),
>
> - SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_OPT_RX_FILTER,
> + SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_TX_COMPLETION,
> SOF_TIMESTAMPING_MASK = (SOF_TIMESTAMPING_LAST - 1) |
> SOF_TIMESTAMPING_LAST
> };
> @@ -58,7 +59,8 @@ enum {
> #define SOF_TIMESTAMPING_TX_RECORD_MASK (SOF_TIMESTAMPING_TX_HARDWARE | \
> SOF_TIMESTAMPING_TX_SOFTWARE | \
> SOF_TIMESTAMPING_TX_SCHED | \
> - SOF_TIMESTAMPING_TX_ACK)
> + SOF_TIMESTAMPING_TX_ACK | \
> + SOF_TIMESTAMPING_TX_COMPLETION)
>
> /**
> * struct so_timestamping - SO_TIMESTAMPING parameter
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index ab8acb737b93..6cbf77bc61fc 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5523,6 +5523,8 @@ static bool skb_tstamp_tx_report_so_timestamping(struct sk_buff *skb,
> SKBTX_SW_TSTAMP);
> case SCM_TSTAMP_ACK:
> return TCP_SKB_CB(skb)->txstamp_ack & TSTAMP_ACK_SK;
> + case SCM_TSTAMP_COMPLETION:
> + return skb_shinfo(skb)->tx_flags & SKBTX_COMPLETION_TSTAMP;
> }
>
> return false;
> diff --git a/net/ethtool/common.c b/net/ethtool/common.c
> index 7e3c16856c1a..0cb6da1f692a 100644
> --- a/net/ethtool/common.c
> +++ b/net/ethtool/common.c
> @@ -476,6 +476,7 @@ const char sof_timestamping_names[][ETH_GSTRING_LEN] = {
> [const_ilog2(SOF_TIMESTAMPING_BIND_PHC)] = "bind-phc",
> [const_ilog2(SOF_TIMESTAMPING_OPT_ID_TCP)] = "option-id-tcp",
> [const_ilog2(SOF_TIMESTAMPING_OPT_RX_FILTER)] = "option-rx-filter",
> + [const_ilog2(SOF_TIMESTAMPING_TX_COMPLETION)] = "tx-completion",
> };
> static_assert(ARRAY_SIZE(sof_timestamping_names) == __SOF_TIMESTAMPING_CNT);
>
> diff --git a/net/socket.c b/net/socket.c
> index b64ecf2722e7..e3d879b53278 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -689,6 +689,9 @@ void __sock_tx_timestamp(__u32 tsflags, __u8 *tx_flags)
> if (tsflags & SOF_TIMESTAMPING_TX_SCHED)
> flags |= SKBTX_SCHED_TSTAMP;
>
> + if (tsflags & SOF_TIMESTAMPING_TX_COMPLETION)
> + flags |= SKBTX_COMPLETION_TSTAMP;
> +
> *tx_flags = flags;
> }
> EXPORT_SYMBOL(__sock_tx_timestamp);
> --
> 2.48.1
>
>
