Re: [RFC PATCH bpf-next v6 1/3] net: Rename mono_delivery_time to tstamp_type for scalabilty

["Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>]

On 5/6/2024 11:51 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 on enum defined
>> in 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 tstamp_type to distinguish between mono and real time.
>>
>> Also skb_set_delivery_type_by_clockid is a new function which accepts
>> clockid to determine the tstamp_type.
>>
>> 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 v5
>> - Avoided using garble function names as mentioned by
>>   Willem.
>> - Implemented a conversion function stead of duplicating 
>>   the same logic as mentioned by Willem.
>> - Fixed indentation problems and minor documentation issues
>>   which mentions tstamp_type as a whole instead of bitfield
>>   notations. (Mentioned both by Willem and Martin)
>>   
>> Changes since v4
>> - Introduce new function to directly delivery_time and
>>   another to set tstamp_type based on clockid. 
>> - Removed un-necessary comments in skbuff.h as 
>>   enums were obvious and understood.
>>
>> Changes since v3
>> - Fixed inconsistent capitalization in skbuff.h
>> - remove reference to MONO_DELIVERY_TIME_MASK in skbuff.h
>>   and point it to skb_tstamp_type now.
>> - Explicitely setting SKB_CLOCK_MONO if valid transmit_time
>>   ip_send_unicast_reply 
>> - Keeping skb_tstamp inline with skb_clear_tstamp. 
>> - skb_set_delivery_time checks if timstamp is 0 and 
>>   sets the tstamp_type to SKB_CLOCK_REAL.
>> - Above comments are given by Willem 
>> - Found out that skbuff.h has access to uapi/linux/time.h
>>   So now instead of using  CLOCK_REAL/CLOCK_MONO 
>>   i am checking actual clockid_t directly to set tstamp_type 
>>   example:- CLOCK_REALTIME/CLOCK_MONOTONIC 
>> - Compilation error fixed in 
>>   net/ieee802154/6lowpan/reassembly.c
>>
>> 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                     | 53 ++++++++++++++++------
>>  include/net/inet_frag.h                    |  4 +-
>>  net/bridge/netfilter/nf_conntrack_bridge.c |  6 +--
>>  net/core/dev.c                             |  2 +-
>>  net/core/filter.c                          | 10 ++--
>>  net/ieee802154/6lowpan/reassembly.c        |  2 +-
>>  net/ipv4/inet_fragment.c                   |  2 +-
>>  net/ipv4/ip_fragment.c                     |  2 +-
>>  net/ipv4/ip_output.c                       |  9 ++--
>>  net/ipv4/tcp_output.c                      | 16 +++----
>>  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 +-
>>  17 files changed, 80 insertions(+), 52 deletions(-)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index 1c2902eaebd3..de3915e2bfdb 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -706,6 +706,11 @@ typedef unsigned int sk_buff_data_t;
>>  typedef unsigned char *sk_buff_data_t;
>>  #endif
>>  
>> +enum skb_tstamp_type {
>> +	SKB_CLOCK_REALTIME,
>> +	SKB_CLOCK_MONOTONIC,
>> +};
>> +
>>  /**
>>   * DOC: Basic sk_buff geometry
>>   *
>> @@ -823,10 +828,9 @@ 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.
>> + *	@tstamp_type: When set, skb->tstamp has the
>> + *		delivery_time in mono clock base Otherwise, the
>> + *		timestamp is considered real clock base.
> 
> Missing period. More importantly, no longer conditional. It always
> captures the type of skb->tstamp.
> 
I think i should move the patchset 2 documentation to this patch itself. 

@tstamp_type: When set, skb->tstamp has the
+ *		delivery_time clock base of skb->tstamp.
>> --- a/net/ipv4/tcp_output.c
>> +++ b/net/ipv4/tcp_output.c
>> @@ -1301,7 +1301,7 @@ 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_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
>> +	skb_set_delivery_type_by_clockid(skb, tp->tcp_wstamp_ns, CLOCK_MONOTONIC);
>>  	if (clone_it) {
>>  		oskb = skb;
>>  
>> @@ -1655,7 +1655,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
>>  
>>  	skb_split(skb, buff, len);
>>  
>> -	skb_set_delivery_time(buff, skb->tstamp, true);
>> +	skb_set_delivery_type_by_clockid(buff, skb->tstamp, CLOCK_MONOTONIC);
>>  	tcp_fragment_tstamp(skb, buff);
> 
> All these hardcoded monotonic calls in TCP can be the shorter version
> 
>     skb_set_delivery_type(.., SKB_CLOCK_MONOTONIC);
I think i should directly call skb_set_delivery_time if i know that TCP always uses Monotonic clock base, 
rather than calling the wrapper api which does nothing but switch and then calls skb_set_delivery_Time. 

Makes sense. I will make the changes in v7 . 
>