Commit a1ac9c8a authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by David S. Miller
Browse files

net: Add skb->mono_delivery_time to distinguish mono delivery_time from (rcv) timestamp 

skb->tstamp was first used as the (rcv) timestamp.
The major usage is to report it to the user (e.g. SO_TIMESTAMP).

Later, skb->tstamp is also set as the (future) delivery_time (e.g. EDT in TCP)
during egress and used by the qdisc (e.g. sch_fq) to make decision on when
the skb can be passed to the dev.

Currently, there is no way to tell skb->tstamp having the (rcv) timestamp
or the delivery_time, so it is always reset to 0 whenever forwarded
between egress and ingress.

While it makes sense to always clear the (rcv) timestamp in skb->tstamp
to avoid confusing sch_fq that expects the delivery_time, it is a
performance issue [0] to clear the delivery_time if the skb finally
egress to a fq@phy-dev.  For example, when forwarding from egress to
ingress and then finally back to egress:

            tcp-sender => veth@netns => veth@hostns => fq@eth0@hostns
                                     ^              ^
                                     reset          rest

This patch adds one bit skb->mono_delivery_time to flag the skb->tstamp
is storing the mono delivery_time (EDT) instead of the (rcv) timestamp.

The current use case is to keep the TCP mono delivery_time (EDT) and
to be used with sch_fq.  A latter patch will also allow tc-bpf@ingress
to read and change the mono delivery_time.

In the future, another bit (e.g. skb->user_delivery_time) can be added
for the SCM_TXTIME where the clock base is tracked by sk->sk_clockid.

[ This patch is a prep work.  The following patches will
  get the other parts of the stack ready first.  Then another patch
  after that will finally set the skb->mono_delivery_time. ]

skb_set_delivery_time() function is added.  It is used by the tcp_output.c
and during ip[6] fragmentation to assign the delivery_time to
the skb->tstamp and also set the skb->mono_delivery_time.

A note on the change in ip_send_unicast_reply() in ip_output.c.
It is only used by TCP to send reset/ack out of a ctl_sk.
Like the new skb_set_delivery_time(), this patch sets
the skb->mono_delivery_time to 0 for now as a place
holder.  It will be enabled in a latter patch.
A similar case in tcp_ipv6 can be done with
skb_set_delivery_time() in tcp_v6_send_response().

[0] (slide 22): https://linuxplumbersconf.org/event/11/contributions/953/attachments/867/1658/LPC_2021_BPF_Datapath_Extensions.pdf



Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 6fb8661c

include/linux/skbuff.h

+13 −0
Original line number Diff line number Diff line
@@ -795,6 +795,10 @@ 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

 *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the

 *		skb->tstamp has the (rcv) timestamp at ingress and

 *		delivery_time at egress.

 *	@napi_id: id of the NAPI struct this skb came from

 *	@sender_cpu: (aka @napi_id) source CPU in XPS

 *	@secmark: security marking
@@ -965,6 +969,7 @@ struct sk_buff { 
	__u8			decrypted:1;

#endif

	__u8			slow_gro:1;

	__u8			mono_delivery_time:1;



#ifdef CONFIG_NET_SCHED

	__u16			tc_index;	/* traffic control index */
@@ -3983,6 +3988,14 @@ static inline ktime_t net_timedelta(ktime_t t) 
	return ktime_sub(ktime_get_real(), t);

}



static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,

					 bool mono)

{

	skb->tstamp = kt;

	/* Setting mono_delivery_time will be enabled later */

	skb->mono_delivery_time = 0;

}



static inline u8 skb_metadata_len(const struct sk_buff *skb)

{

	return skb_shinfo(skb)->meta_len;

net/bridge/netfilter/nf_conntrack_bridge.c

+3 −2
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk, 
					   struct sk_buff *))

{

	int frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;

	bool mono_delivery_time = skb->mono_delivery_time;

	unsigned int hlen, ll_rs, mtu;

	ktime_t tstamp = skb->tstamp;

	struct ip_frag_state state;
@@ -81,7 +82,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk, 
			if (iter.frag)

				ip_fraglist_prepare(skb, &iter);



			skb->tstamp = tstamp;

			skb_set_delivery_time(skb, tstamp, mono_delivery_time);

			err = output(net, sk, data, skb);

			if (err || !iter.frag)

				break;
@@ -112,7 +113,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk, 
			goto blackhole;

		}



		skb2->tstamp = tstamp;

		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);

		err = output(net, sk, data, skb2);

		if (err)

			goto blackhole;

net/ipv4/ip_output.c

+5 −2
Original line number Diff line number Diff line
@@ -761,6 +761,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
{

	struct iphdr *iph;

	struct sk_buff *skb2;

	bool mono_delivery_time = skb->mono_delivery_time;

	struct rtable *rt = skb_rtable(skb);

	unsigned int mtu, hlen, ll_rs;

	struct ip_fraglist_iter iter;
@@ -852,7 +853,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
				}

			}



			skb->tstamp = tstamp;

			skb_set_delivery_time(skb, tstamp, mono_delivery_time);

			err = output(net, sk, skb);



			if (!err)
@@ -908,7 +909,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
		/*

		 *	Put this fragment into the sending queue.

		 */

		skb2->tstamp = tstamp;

		skb_set_delivery_time(skb2, tstamp, mono_delivery_time);

		err = output(net, sk, skb2);

		if (err)

			goto fail;
@@ -1727,6 +1728,8 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb, 
			  arg->csumoffset) = csum_fold(csum_add(nskb->csum,

								arg->csum));

		nskb->ip_summed = CHECKSUM_NONE;

		/* Setting mono_delivery_time will be enabled later */

		nskb->mono_delivery_time = 0;

		ip_push_pending_frames(sk, &fl4);

	}

out:

net/ipv4/tcp_output.c

+9 −7
Original line number Diff line number Diff line
@@ -1253,7 +1253,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, 
	tp = tcp_sk(sk);

	prior_wstamp = tp->tcp_wstamp_ns;

	tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);

	skb->skb_mstamp_ns = tp->tcp_wstamp_ns;

	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);

	if (clone_it) {

		oskb = skb;
@@ -1589,7 +1589,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue, 


	skb_split(skb, buff, len);



	buff->tstamp = skb->tstamp;

	skb_set_delivery_time(buff, skb->tstamp, true);

	tcp_fragment_tstamp(skb, buff);



	old_factor = tcp_skb_pcount(skb);
@@ -2616,7 +2616,8 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 


		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {

			/* "skb_mstamp_ns" is used as a start point for the retransmit timer */

			skb->skb_mstamp_ns = tp->tcp_wstamp_ns = tp->tcp_clock_cache;

			tp->tcp_wstamp_ns = tp->tcp_clock_cache;

			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);

			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);

			tcp_init_tso_segs(skb, mss_now);

			goto repair; /* Skip network transmission */
@@ -3541,11 +3542,12 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, 
	now = tcp_clock_ns();

#ifdef CONFIG_SYN_COOKIES

	if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok))

		skb->skb_mstamp_ns = cookie_init_timestamp(req, now);

		skb_set_delivery_time(skb, cookie_init_timestamp(req, now),

				      true);

	else

#endif

	{

		skb->skb_mstamp_ns = now;

		skb_set_delivery_time(skb, now, true);

		if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */

			tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);

	}
@@ -3594,7 +3596,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, 
	bpf_skops_write_hdr_opt((struct sock *)sk, skb, req, syn_skb,

				synack_type, &opts);



	skb->skb_mstamp_ns = now;

	skb_set_delivery_time(skb, now, true);

	tcp_add_tx_delay(skb, tp);



	return skb;
@@ -3771,7 +3773,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) 


	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);



	syn->skb_mstamp_ns = syn_data->skb_mstamp_ns;

	skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, true);



	/* Now full SYN+DATA was cloned and sent (or not),

	 * remove the SYN from the original skb (syn_data)

net/ipv6/ip6_output.c

+3 −2
Original line number Diff line number Diff line
@@ -813,6 +813,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
	struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);

	struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?

				inet6_sk(skb->sk) : NULL;

	bool mono_delivery_time = skb->mono_delivery_time;

	struct ip6_frag_state state;

	unsigned int mtu, hlen, nexthdr_offset;

	ktime_t tstamp = skb->tstamp;
@@ -903,7 +904,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
			if (iter.frag)

				ip6_fraglist_prepare(skb, &iter);



			skb->tstamp = tstamp;

			skb_set_delivery_time(skb, tstamp, mono_delivery_time);

			err = output(net, sk, skb);

			if (!err)

				IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
@@ -962,7 +963,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
		/*

		 *	Put this fragment into the sending queue.

		 */

		frag->tstamp = tstamp;

		skb_set_delivery_time(frag, tstamp, mono_delivery_time);

		err = output(net, sk, frag);

		if (err)

			goto fail;