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Date: Mon, 15 Apr 2024 16:46:49 -0400
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>, 
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>, 
 "David S. Miller" <davem@davemloft.net>, 
 Eric Dumazet <edumazet@google.com>, 
 Jakub Kicinski <kuba@kernel.org>, 
 Paolo Abeni <pabeni@redhat.com>, 
 netdev@vger.kernel.org, 
 linux-kernel@vger.kernel.org, 
 Andrew Halaney <ahalaney@redhat.com>, 
 Martin KaFai Lau <martin.lau@kernel.org>, 
 Martin KaFai Lau <martin.lau@linux.dev>, 
 Daniel Borkmann <daniel@iogearbox.net>, 
 bpf <bpf@vger.kernel.org>
Cc: kernel@quicinc.com
Message-ID: <661d92391de45_30101294f2@willemb.c.googlers.com.notmuch>
In-Reply-To: <c992e03b-eee5-471a-9002-f35bdfa1be2d@quicinc.com>
References: <20240412210125.1780574-1-quic_abchauha@quicinc.com>
 <20240412210125.1780574-2-quic_abchauha@quicinc.com>
 <661ad4f0e3766_3be9a7294a1@willemb.c.googlers.com.notmuch>
 <c992e03b-eee5-471a-9002-f35bdfa1be2d@quicinc.com>
Subject: Re: [RFC PATCH bpf-next v3 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty
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Abhishek Chauhan (ABC) wrote:
> 
> 
> On 4/13/2024 11:54 AM, Willem de Bruijn wrote:
> > Abhishek Chauhan wrote:
> >> mono_delivery_time was added to check if skb->tstamp has delivery
> >> time in mono clock base (i.e. EDT) otherwise skb->tstamp has
> >> timestamp in ingress and delivery_time at egress.
> >>
> >> Renaming the bitfield from mono_delivery_time to tstamp_type is for
> >> extensibilty for other timestamps such as userspace timestamp
> >> (i.e. SO_TXTIME) set via sock opts.
> >>
> >> As we are renaming the mono_delivery_time to tstamp_type, it makes
> >> sense to start assigning tstamp_type based out if enum defined as
> >> part of this commit
> >>
> >> Earlier we used bool arg flag to check if the tstamp is mono in
> >> function skb_set_delivery_time, Now the signature of the functions
> >> accepts enum to distinguish between mono and real time
> >>
> >> Bridge driver today has no support to forward the userspace timestamp
> >> packets and ends up resetting the timestamp. ETF qdisc checks the
> >> packet coming from userspace and encounters to be 0 thereby dropping
> >> time sensitive packets. These changes will allow userspace timestamps
> >> packets to be forwarded from the bridge to NIC drivers.
> >>
> >> In future tstamp_type:1 can be extended to support userspace timestamp
> >> by increasing the bitfield.
> >>
> >> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
> >> Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
> >> ---
> >> Changes since v2
> >> - Minor changes to commit subject
> >>
> >> Changes since v1
> >> - Squashed the two commits into one as mentioned by Willem.
> >> - Introduced switch in skb_set_delivery_time.
> >> - Renamed and removed directionality aspects w.r.t tstamp_type 
> >>   as mentioned by Willem.
> >>
> >>  include/linux/skbuff.h                     | 33 +++++++++++++++-------
> >>  include/net/inet_frag.h                    |  4 +--
> >>  net/bridge/netfilter/nf_conntrack_bridge.c |  6 ++--
> >>  net/core/dev.c                             |  2 +-
> >>  net/core/filter.c                          |  8 +++---
> >>  net/ipv4/inet_fragment.c                   |  2 +-
> >>  net/ipv4/ip_fragment.c                     |  2 +-
> >>  net/ipv4/ip_output.c                       |  8 +++---
> >>  net/ipv4/tcp_output.c                      | 14 ++++-----
> >>  net/ipv6/ip6_output.c                      |  6 ++--
> >>  net/ipv6/netfilter.c                       |  6 ++--
> >>  net/ipv6/netfilter/nf_conntrack_reasm.c    |  2 +-
> >>  net/ipv6/reassembly.c                      |  2 +-
> >>  net/ipv6/tcp_ipv6.c                        |  2 +-
> >>  net/sched/act_bpf.c                        |  4 +--
> >>  net/sched/cls_bpf.c                        |  4 +--
> >>  16 files changed, 59 insertions(+), 46 deletions(-)
> >>
> >> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> >> index 7135a3e94afd..a83a2120b57f 100644
> >> --- a/include/linux/skbuff.h
> >> +++ b/include/linux/skbuff.h
> >> @@ -702,6 +702,11 @@ typedef unsigned int sk_buff_data_t;
> >>  typedef unsigned char *sk_buff_data_t;
> >>  #endif
> >>  
> >> +enum skb_tstamp_type {
> >> +	CLOCK_REAL = 0, /* Time base is realtime */
> >> +	CLOCK_MONO = 1, /* Time base is Monotonic */
> >> +};
> > 
> > Minor: inconsistent capitalization
> > 
> I will fix this. 
> 
> >> +
> >>  /**
> >>   * DOC: Basic sk_buff geometry
> >>   *
> >> @@ -819,7 +824,7 @@ typedef unsigned char *sk_buff_data_t;
> >>   *	@dst_pending_confirm: need to confirm neighbour
> >>   *	@decrypted: Decrypted SKB
> >>   *	@slow_gro: state present at GRO time, slower prepare step required
> >> - *	@mono_delivery_time: When set, skb->tstamp has the
> >> + *	@tstamp_type: When set, skb->tstamp has the
> >>   *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
> >>   *		skb->tstamp has the (rcv) timestamp at ingress and
> >>   *		delivery_time at egress.
> >> @@ -950,7 +955,7 @@ struct sk_buff {
> >>  	/* private: */
> >>  	__u8			__mono_tc_offset[0];
> >>  	/* public: */
> >> -	__u8			mono_delivery_time:1;	/* See SKB_MONO_DELIVERY_TIME_MASK */
> >> +	__u8			tstamp_type:1;	/* See SKB_MONO_DELIVERY_TIME_MASK */
> > 
> > Also remove reference to MONO_DELIVERY_TIME_MASK, or instead refer to
> > skb_tstamp_type.
> > 
> >>  #ifdef CONFIG_NET_XGRESS
> >>  	__u8			tc_at_ingress:1;	/* See TC_AT_INGRESS_MASK */
> >>  	__u8			tc_skip_classify:1;
> >> @@ -4237,7 +4242,7 @@ static inline void skb_get_new_timestampns(const struct sk_buff *skb,
> >>  static inline void __net_timestamp(struct sk_buff *skb)
> >>  {
> >>  	skb->tstamp = ktime_get_real();
> >> -	skb->mono_delivery_time = 0;
> >> +	skb->tstamp_type = CLOCK_REAL;
> >>  }
> >>  
> >>  static inline ktime_t net_timedelta(ktime_t t)
> >> @@ -4246,10 +4251,18 @@ static inline ktime_t net_timedelta(ktime_t t)
> >>  }
> >>  
> >>  static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
> >> -					 bool mono)
> >> +					  u8 tstamp_type)
> >>  {
> >>  	skb->tstamp = kt;
> >> -	skb->mono_delivery_time = kt && mono;
> >> +
> >> +	switch (tstamp_type) {
> >> +	case CLOCK_REAL:
> >> +		skb->tstamp_type = CLOCK_REAL;
> >> +		break;
> >> +	case CLOCK_MONO:
> >> +		skb->tstamp_type = kt && tstamp_type;
> >> +		break;
> >> +	}
> > 
> > Technically this leaves the tstamp_type undefined if (skb, 0, CLOCK_REAL)
> Do you think i should be checking for valid value of tstamp before setting the tstamp_type ? Only then set it. 

A kt of 0 is interpreted as resetting the type. That should probably
be maintained.

For SO_TIMESTAMPING, a mono delivery time of 0 does have some meaning.
In __sock_recv_timestamp:

        /* Race occurred between timestamp enabling and packet
           receiving.  Fill in the current time for now. */
        if (need_software_tstamp && skb->tstamp == 0) {
                __net_timestamp(skb);
                false_tstamp = 1;
        }