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Message-ID: <6bfee126-36f4-4595-950e-058d93303362@quicinc.com>
Date: Mon, 15 Apr 2024 14:06:45 -0700
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Subject: Re: [RFC PATCH bpf-next v3 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty
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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>
 <c992e03b-eee5-471a-9002-f35bdfa1be2d@quicinc.com>
 <661d92391de45_30101294f2@willemb.c.googlers.com.notmuch>
From: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>
In-Reply-To: <661d92391de45_30101294f2@willemb.c.googlers.com.notmuch>
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On 4/15/2024 1:46 PM, Willem de Bruijn wrote:
> 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;
>         }

Well in that case the above logic still resets the tstamp and sets the tstamp_type to CLOCK_REAL(value 0). 
Anyway the tstamp_type will be 0 to begin with. 
The logic is still inline with previous implementation, because previously if kt was 0 then kt && mono sets the tstamp_type (previously called as mono_delivery_time) to 0 (i.e SKB_CLOCK_REAL).