Re: [PATCH net-next v3] net: Re-use and set mono_delivery_time bit for userspace tstamp packets

[Abhishek Chauhan (ABC)]

On 3/1/2024 10:45 AM, Willem de Bruijn wrote:
> Abhishek Chauhan wrote:
>> 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.
>>
>> Setting the same bit (mono_delivery_time) to avoid dropping of
>> userspace tstamp packets in the forwarding path.
>>
>> Existing functionality of mono_delivery_time remains unaltered here,
>> instead just extended with userspace tstamp support for bridge
>> forwarding path.
>>
>> Signed-off-by: Abhishek Chauhan <quic_abchauha@xxxxxxxxxxx>
>> ---
>> Changes since v2
>> - Updated the commit subject and message. 
>> - Took care of few comments from Willem to re-use mono_delivery_time
>>   with comments and documentations in the header and source file.
>> - Took care of comment from Andrew on the typo in the comment.
>> - Existing self-test test cases are executed to make sure existing 
>>   implementation is not impacted as stated by Paolo.(so_txtime.sh). 
>> - Internal validation of UDP packets using iperf/so_priority/so_txtime
>>   with MQPRIO + ETF offload is executed as well.
>> - Test case is included below
>>
>> Test 1 :- FQ + ETF (SW path)
>>
>> [root@ecbldauto-lvarm04-lnx ~]# ./so_txtime.sh
>> [  280.640551] q->last time is 1707955476143297550
>> [  283.338947] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>> [  284.078429] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>>
>> SO_TXTIME ipv4 clock monotonic
>> payload:a delay:109 expected:0 (us)
>>
>> SO_TXTIME ipv6 clock monotonic
>> payload:a delay:140 expected:0 (us)
>>
>> SO_TXTIME ipv6 clock monotonic
>> payload:a delay:12739 expected:10000 (us)
>>
>> SO_TXTIME ipv4 clock monotonic
>> payload:a delay:10054 expected:10000 (us)
>> payload:b delay:20043 expected:20000 (us)
>>
>> SO_TXTIME ipv6 clock monotonic
>> payload:b delay:20078 expected:20000 (us)
>> payload:a delay:20177 expected:20000 (us)
>>
>> SO_TXTIME ipv4 clock tai
>> send: pkt a at -1707955482913ms dropped: invalid txtime
>> [  287.070504] now is set to 1707955482913404839
>> [  287.070509] tx time from SKB is 0
>> ./so_txtime: recv: timeout: Resource temporarily unavailable
>>
>> SO_TXTIME ipv6 clock tai
>> send: pkt a at 0ms dropped: invalid txtime
>> [  287.070510] q->last time is 0
>> [  287.420590] now is set to 1707955483263491298
>> [  287.420596] tx time from SKB is 1707955483263454527
>> ./so_txtime: recv: timeout: Resource temporarily unavailable
>>
>> SO_TXTIME ipv6 clock tai
>> [  287.420597] q->last time is 0
>> [  287.700598] now is set to 1707955483543498954
>> [  287.700604] tx time from SKB is 1707955483553463173
>> payload:a delay:9655 expected:10000 (us)
>>
>> SO_TXTIME ipv4 clock tai
>> [  287.700605] q->last time is 0
>> [  288.100532] now is set to 1707955483943432391
>> [  288.100537] tx time from SKB is 1707955483953413016
>> payload:a delay:9668 expected:10000 (us)[  288.100538] q->last time is 1707955483553463173
>>
>> [  288.100546] now is set to 1707955483943446975
>> [  288.100547] tx time from SKB is 1707955483963413016
>> payload:b delay:20484 expected:20000 (us)
>>
>> SO_TXTIME ipv6 clock tai
>> [  288.100547] q->last time is 1707955483553463173
>> [  288.440582] now is set to 1707955484283482495
>> [  288.440587] tx time from SKB is 1707955484303452808
>> payload:b delay:9648 expected:10000 (us)[  288.440588] q->last time is 1707955483963413016
>>
>> [  288.440598] now is set to 1707955484283499370
>> payload:a delay:22037 expected:20000 (us)
>> [  288.440599] tx time from SKB is 1707955484293452808
>> OK. All tests passed
>>
>>
>> Test case 2 (MQPRIO + ETF HW offload)
>>
>> [root@ecbldauto-lvarm04-lnx ~]# tc qdisc add dev eth0 handle 100: parent root mqprio num_tc 4 \
>>             map 0 2 1 3 3 2 2 2 2 2 2 2 2 2 2 2 \
>>             queues 1@0 1@1 1@2 1@3\
>>             hw 0
>> [root@ecbldauto-lvarm04-lnx ~]#
>> tc qdisc replace dev eth0 parent 100:4 etf \
>>             clockid CLOCK_TAI delta 40000  offload skip_sock_check
>> [   89.145838] qcom-ethqos 23040000.ethernet eth0: enabled ETF for Queue test log 3, number of queues 4, qopt enable 1, tbs queue bit 1
>> [   89.145846] qcom-ethqos 23040000.ethernet eth0: enabled ETF for Queue 3
>>
>>
>> [root@ecbldauto-lvarm04-lnx ~]# ./a.out -4 -c tai -S 192.168.1.1 -D 192.168.1.2 a,1,b,2
>>
>> SO_TXTIME ipv4 clock tai
>>
>>  glob_tstat = 1707955395256170394
>> [  199.623650] now is set to 1707955395256215810
>> [  199.623655] tx time from SKB is 1707955395257170394
>> [  199.623656] q->last time is 0
>> [  199.623663] now is set to 1707955395256230029
>> [  199.623664] tx time from SKB is 1707955395258170394
>> [  199.623665] q->last time is 0
>> [  199.624589] qcom-ethqos 23040000.ethernet eth0: emac ethqos tx_xmit : lauching tbs packet at 1707955395 sec and 257170394 nsec
>> [  199.625573] qcom-ethqos 23040000.ethernet eth0: emac ethqos tx_xmit : lauching tbs packet at 1707955395 sec and 258170394 nsec
>>
>> Changes since v1 
>> - Changed the commit subject as i am modifying the mono_delivery_time 
>>   bit with clockid_delivery_time.
>> - Took care of suggestion mentioned by Willem to use the same bit for 
>>   userspace delivery time as there are no conflicts between TCP and 
>>   SCM_TXTIME, because explicit cmsg makes no sense for TCP and only
>>   RAW and DGRAM sockets interprets it. 
>> - Clear explaination of why this is needed mentioned below and this 
>>   is extending the work done by Martin for mono_delivery_time 
>>   https://patchwork.kernel.org/project/netdevbpf/patch/20220302195525.3480280-1-kafai@xxxxxx/
>> - Version 1 patch can be referenced with below link which states 
>>   the exact problem with tc-etf and discussions which took place
>>   https://lore.kernel.org/all/20240215215632.2899370-1-quic_abchauha@xxxxxxxxxxx/
>>
>>  include/linux/skbuff.h | 4 ++++
>>  net/ipv4/ip_output.c   | 7 +++++++
>>  net/ipv4/raw.c         | 7 +++++++
>>  net/ipv6/ip6_output.c  | 8 +++++++-
>>  net/ipv6/raw.c         | 8 +++++++-
>>  net/packet/af_packet.c | 8 +++++++-
>>  6 files changed, 39 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index 2dde34c29203..58586d56b19f 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -820,6 +820,10 @@ typedef unsigned char *sk_buff_data_t;
>>   *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
>>   *		skb->tstamp has the (rcv) timestamp at ingress and
>>   *		delivery_time at egress.
>> + *		This bit is also set for tstamp coming from userspace which
>> + *		acts as an information in the bridge forwarding path to avoid
>> + *		resetting the tstamp value when user sets the timestamp using
>> + *		SO_TXTIME sockopts.
> 
> There are multiple applications of this information aside from
> bridging. I'd drop that and instead rewrite the existing. Something
> like
> 
> "delivery_time in mono clock base (i.e., EDT) or a clock base chosen
> by SO_TXTIME. If zero, skb->tstamp has the (rcv) timestamp at
> ingress."
> 

Will make the changes accordingly. 

>>   *	@napi_id: id of the NAPI struct this skb came from
>>   *	@sender_cpu: (aka @napi_id) source CPU in XPS
>>   *	@alloc_cpu: CPU which did the skb allocation.
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index 5b5a0adb927f..4ae6aea8f8d6 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -1455,6 +1455,13 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>>  	skb->priority = (cork->tos != -1) ? cork->priority: READ_ONCE(sk->sk_priority);
>>  	skb->mark = cork->mark;
>>  	skb->tstamp = cork->transmit_time;
>> +	/* Timestamp coming from userspace using CMSG is stored as part
>> +	 * of transmit_time as part of cork. To ensure bridge does not
>> +	 * drop the tstamp in the forwarding path.We are reusing bit
>> +	 * mono_delivery_time to avoid reset of tstamp in bridge
>> +	 * forwarding path.
>> +	 */
>> +	skb->mono_delivery_time = !!skb->tstamp;
> 
> This patch adds too much verbose commentary, repeated multiple times,
> for such a small change. Keep only the comment in skbuff.h.
> 

Got it. I was thinking of the same. I will make the change. 

>>  	/*
>>  	 * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
>>  	 * on dst refcount
>> diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
>> index aea89326c697..6e67c0203be8 100644
>> --- a/net/ipv4/raw.c
>> +++ b/net/ipv4/raw.c
>> @@ -353,6 +353,13 @@ static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
>>  	skb->priority = READ_ONCE(sk->sk_priority);
>>  	skb->mark = sockc->mark;
>>  	skb->tstamp = sockc->transmit_time;
>> +	/* Timestamp coming from userspace using CMSG is stored as part
>> +	 * of transmit_time as part of sockcmcookie. To ensure bridge does not
>> +	 * drop the tstamp in the forwarding path. We are reusing bit
>> +	 * mono_delivery_time to avoid reset of tstamp in bridge
>> +	 * forwarding path.
>> +	 */
>> +	skb->mono_delivery_time = !!skb->tstamp;
>>  	skb_dst_set(skb, &rt->dst);
>>  	*rtp = NULL;
>>  
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index a722a43dd668..f5b5e13a920f 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -1922,7 +1922,13 @@ struct sk_buff *__ip6_make_skb(struct sock *sk,
>>  	skb->priority = READ_ONCE(sk->sk_priority);
>>  	skb->mark = cork->base.mark;
>>  	skb->tstamp = cork->base.transmit_time;
>> -
>> +	/* Timestamp coming from userspace using CMSG is stored as part
>> +	 * of transmit_time as part of cork. To ensure bridge does not
>> +	 * drop the tstamp in the forwarding path. We are reusing bit
>> +	 * mono_delivery_time to avoid reset of tstamp in bridge
>> +	 * forwarding path.
>> +	 */
>> +	skb->mono_delivery_time = !!skb->tstamp;
>>  	ip6_cork_steal_dst(skb, cork);
>>  	IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTREQUESTS);
>>  	if (proto == IPPROTO_ICMPV6) {
>> diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
>> index 03dbb874c363..d2e2a1ec3de4 100644
>> --- a/net/ipv6/raw.c
>> +++ b/net/ipv6/raw.c
>> @@ -616,7 +616,13 @@ static int rawv6_send_hdrinc(struct sock *sk, struct msghdr *msg, int length,
>>  	skb->priority = READ_ONCE(sk->sk_priority);
>>  	skb->mark = sockc->mark;
>>  	skb->tstamp = sockc->transmit_time;
>> -
>> +	/* Timestamp coming from userspace using CMSG is stored as part
>> +	 * of transmit_time as part of sockcmcookie. To ensure bridge does not
>> +	 * drop the tstamp in the forwarding path.We are reusing bit
>> +	 * mono_delivery_time to avoid reset of tstamp in bridge
>> +	 * forwarding path.
>> +	 */
>> +	skb->mono_delivery_time = !!skb->tstamp;
>>  	skb_put(skb, length);
>>  	skb_reset_network_header(skb);
>>  	iph = ipv6_hdr(skb);
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index c9bbc2686690..949e936b5786 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -2057,7 +2057,13 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg,
>>  	skb->priority = READ_ONCE(sk->sk_priority);
>>  	skb->mark = READ_ONCE(sk->sk_mark);
>>  	skb->tstamp = sockc.transmit_time;
>> -
>> +	/* Timestamp coming from userspace using CMSG is stored as part
>> +	 * of transmit_time as part of sockcmcookie. To ensure bridge does not
>> +	 * drop the tstamp in the forwarding path. We are reusing bit
>> +	 * mono_delivery_time to avoid reset of tstamp in bridge
>> +	 * forwarding path.
>> +	 */
>> +	skb->mono_delivery_time = !!skb->tstamp;
> 
> Search for all occurrences of skb->tstamp getting initialized from
> sockc.transmit_time. af_packet.c has three such cases.
> 

Let me check and add at every instance. 

>>  	skb_setup_tx_timestamp(skb, sockc.tsflags);
>>  
>>  	if (unlikely(extra_len == 4))
>> -- 
>> 2.25.1
>>
> 
>