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Date: Thu, 13 Apr 2017 10:30:32 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Miroslav Lichvar <mlichvar@...hat.com>
Cc: Network Development <netdev@...r.kernel.org>,
Richard Cochran <richardcochran@...il.com>,
Willem de Bruijn <willemb@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
"Keller, Jacob E" <jacob.e.keller@...el.com>,
Denny Page <dennypage@...com>, Jiri Benc <jbenc@...hat.com>
Subject: Re: [RFC PATCH 6/7] net: allow simultaneous SW and HW transmit timestamping
On Wed, Apr 12, 2017 at 10:17 AM, Miroslav Lichvar <mlichvar@...hat.com> wrote:
> Add SOF_TIMESTAMPING_OPT_MULTIMSG option to allow looping the outgoing
> packet to the socket's error queue with a software timestamp even when
> a hardware transmit timestamp is expected to be provided by the driver.
>
> Applications using this option will receive two separate messages from
> the error queue, one with a software timestamp and the other with a
> hardware timestamp. As the hardware timestamp is saved to the shared skb
> info, which may happen before the first message with software timestamp
> is received by the application, the hardware timestamp is copied to the
> SCM_TIMESTAMPING control message only when the skb has no software
> timestamp.
>
> CC: Richard Cochran <richardcochran@...il.com>
> CC: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Miroslav Lichvar <mlichvar@...hat.com>
> ---
> Documentation/networking/timestamping.txt | 12 ++++++++++--
> include/linux/skbuff.h | 3 +--
> include/uapi/linux/net_tstamp.h | 3 ++-
> net/core/skbuff.c | 4 ++++
> net/socket.c | 6 ++++++
> 5 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
> index ed04aaa..8f30385 100644
> --- a/Documentation/networking/timestamping.txt
> +++ b/Documentation/networking/timestamping.txt
> @@ -201,6 +201,12 @@ SOF_TIMESTAMPING_OPT_PKTINFO:
> this information, it will be attached in struct scm_ts_pktinfo as
> a separate control message of type SCM_TIMESTAMPING_PKTINFO.
>
> +SOF_TIMESTAMPING_OPT_MULTIMSG:
> +
> + Allow outgoing packets to be looped multiple times to the socket's
> + error queue in order to receive both software and hardware transmit
> + timestamps.
> +
It is already possible to receive multiple copies of the same message.
Timestamps of type SCM_TSTAMP_SCHED will be passed for every
device, virtual or physical, such as bonding. With TCP retransmits,
multiple SCM_TSTAMP_SND can be observed.
The name for this option is therefore not very descriptive. Perhaps
SOF_TIMESTAMPING_OPT_BOTH_SW_HW.
> New applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to
> disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
> regardless of the setting of sysctl net.core.tstamp_allow_data.
> @@ -320,8 +326,10 @@ struct scm_timestamping {
> };
>
> The structure can return up to three timestamps. This is a legacy
> -feature. Only one field is non-zero at any time. Most timestamps
> -are passed in ts[0]. Hardware timestamps are passed in ts[2].
> +feature. Most timestamps are passed in ts[0]. Hardware timestamps
> +are passed in ts[2]. Incoming packets may have timestamps in both
> +ts[0] and ts[2], but for outgoing packets only one field is non-zero
> +at any time.
>
> ts[1] used to hold hardware timestamps converted to system time.
> Instead, expose the hardware clock device on the NIC directly as
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index e91685a..0387c4b 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -3302,8 +3302,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
>
> static inline void sw_tx_timestamp(struct sk_buff *skb)
> {
> - if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP &&
> - !(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS))
> + if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
> skb_tstamp_tx(skb, NULL);
> }
>
> diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
> index 8397ecd..887e3ff 100644
> --- a/include/uapi/linux/net_tstamp.h
> +++ b/include/uapi/linux/net_tstamp.h
> @@ -27,8 +27,9 @@ enum {
> SOF_TIMESTAMPING_OPT_TSONLY = (1<<11),
> SOF_TIMESTAMPING_OPT_STATS = (1<<12),
> SOF_TIMESTAMPING_OPT_PKTINFO = (1<<13),
> + SOF_TIMESTAMPING_OPT_MULTIMSG = (1<<14),
>
> - SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_OPT_PKTINFO,
> + SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_OPT_MULTIMSG,
> SOF_TIMESTAMPING_MASK = (SOF_TIMESTAMPING_LAST - 1) |
> SOF_TIMESTAMPING_LAST
> };
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 7ca251f..d3df8ff 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3863,6 +3863,10 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
> if (!sk)
> return;
>
> + if (!hwtstamps && !(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_MULTIMSG) &&
> + skb_shinfo(orig_skb)->tx_flags & SKBTX_IN_PROGRESS)
> + return;
> +
> tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
> if (!skb_may_tx_timestamp(sk, tsonly))
> return;
> diff --git a/net/socket.c b/net/socket.c
> index 32e78de..5c9f2eb 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -695,12 +695,18 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
> }
> }
>
> + /* Received packets may have both SW and HW timestamps in one control
> + * message. Transmitted packets may have only one timestamp in the
> + * control message, but there may be two separate messages in the error
> + * queue if the SOF_TIMESTAMPING_OPT_MULTIMSG option is enabled.
> + */
Unnecessary comment, and inexact given SCM_TSTAMP_SCHED and others.
> memset(&tss, 0, sizeof(tss));
> if ((sk->sk_tsflags & SOF_TIMESTAMPING_SOFTWARE) &&
> ktime_to_timespec_cond(skb->tstamp, tss.ts + 0))
> empty = 0;
> if (shhwtstamps &&
> (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
> + (empty || !skb_is_err_queue(skb)) &&
> ktime_to_timespec_cond(shhwtstamps->hwtstamp, tss.ts + 2)) {
> if (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_PKTINFO &&
> shhwtstamps->if_index) {
> --
> 2.9.3
>
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