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Message-ID: <c992e03b-eee5-471a-9002-f35bdfa1be2d@quicinc.com>
Date: Mon, 15 Apr 2024 13:27:56 -0700
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Subject: Re: [RFC PATCH bpf-next v3 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty
Content-Language: en-US
To: 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>
References: <20240412210125.1780574-1-quic_abchauha@quicinc.com>
 <20240412210125.1780574-2-quic_abchauha@quicinc.com>
 <661ad4f0e3766_3be9a7294a1@willemb.c.googlers.com.notmuch>
From: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>
In-Reply-To: <661ad4f0e3766_3be9a7294a1@willemb.c.googlers.com.notmuch>
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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. 

>>  }
>>  
>>  DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
>> @@ -4259,8 +4272,8 @@ DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
>>   */
>>  static inline void skb_clear_delivery_time(struct sk_buff *skb)
>>  {
>> -	if (skb->mono_delivery_time) {
>> -		skb->mono_delivery_time = 0;
>> +	if (skb->tstamp_type) {
>> +		skb->tstamp_type = CLOCK_REAL;
>>  		if (static_branch_unlikely(&netstamp_needed_key))
>>  			skb->tstamp = ktime_get_real();
>>  		else
>> @@ -4270,7 +4283,7 @@ static inline void skb_clear_delivery_time(struct sk_buff *skb)
>>  
>>  static inline void skb_clear_tstamp(struct sk_buff *skb)
>>  {
>> -	if (skb->mono_delivery_time)
>> +	if (skb->tstamp_type)
>>  		return;
>>  
>>  	skb->tstamp = 0;
>> @@ -4278,7 +4291,7 @@ static inline void skb_clear_tstamp(struct sk_buff *skb)
>>  
>>  static inline ktime_t skb_tstamp(const struct sk_buff *skb)
>>  {
>> -	if (skb->mono_delivery_time)
>> +	if (skb->tstamp_type == CLOCK_MONO)
>>  		return 0;
> 
> Should this be if (skb->tstamp_type), in line with skb_clear_tstamp,
> right above?
I think so too. I thought i will not alter the existing functionality and keep it as close to the previous working changes. 
> 
>> @@ -1649,7 +1649,7 @@ 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;
>> -		nskb->mono_delivery_time = !!transmit_time;
>> +		nskb->tstamp_type = !!transmit_time;
> 
> In anticipation of more tstamp_types, explicitly set to CLOCK_MONO.
I will set it to SKB_CLOCK_MONO 
> 
>>  		if (txhash)
>>  			skb_set_hash(nskb, txhash, PKT_HASH_TYPE_L4);
>>  		ip_push_pending_frames(sk, &fl4);