linux-kernel - Re: [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to tstamp

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Message-ID: <d25533d6-5d09-4c9f-8801-54ac35db98ed@quicinc.com>
Date: Thu, 18 Apr 2024 13:38:03 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Andrew Halaney <ahalaney@...hat.com>,
        "Martin
 KaFai Lau" <martin.lau@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>
CC: <kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty



On 4/18/2024 1:11 PM, Willem de Bruijn wrote:
> Abhishek Chauhan (ABC) wrote:
>>
>>
>> On 4/18/2024 11:47 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.
>>>>
>>>> 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@...cinc.com>
>>>
>>>> +/**
>>>> + * tstamp_type:1 can take 2 values each
>>>> + * represented by time base in skb
>>>> + * 0x0 => real timestamp_type
>>>> + * 0x1 => mono timestamp_type
>>>> + */
>>>> +enum skb_tstamp_type {
>>>> +	SKB_CLOCK_REAL,	/* Time base is skb is REALTIME */
>>>> +	SKB_CLOCK_MONO,	/* Time base is skb is MONOTONIC */
>>>> +};
>>>> +
>>>
>>> Can drop the comments. These names are self documenting.
>>
>> Noted! . I will take care of this
>>>
>>>>  /**
>>>>   * DOC: Basic sk_buff geometry
>>>>   *
>>>> @@ -819,7 +830,7 @@ 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.
>>>
>>> Is this still correct? I think all egress does now annotate correctly
>>> as SKB_CLOCK_MONO. So when not set it always is SKB_CLOCK_REAL.
>>>
>> That is correct. 
>>
>>>> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
>>>> index 61119d42b0fd..a062f88c47c3 100644
>>>> --- a/net/ipv4/tcp_output.c
>>>> +++ b/net/ipv4/tcp_output.c
>>>> @@ -1300,7 +1300,7 @@ 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_time(skb, tp->tcp_wstamp_ns, CLOCK_MONOTONIC);
>>>
>>> Multiple references to CLOCK_MONOTONIC left
>>>
>> I think i took care of all the references. Apologies if i didn't understand your comment here. 
> 
> On closer read, there is a type issue here.
> 
> skb_set_delivery_time takes a u8 tstamp_type. But it is often passed
> a clockid_t, and that is also what the switch expects.
> 
> But it does also get called with a tstamp_type in code like the
> following:
> 
> +       u8 tstamp_type = skb->tstamp_type;
>         unsigned int hlen, ll_rs, mtu;
>         ktime_t tstamp = skb->tstamp;
>         struct ip_frag_state state;
> @@ -82,7 +82,7 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
>                         if (iter.frag)
>                                 ip_fraglist_prepare(skb, &iter);
>   
> -                       skb_set_delivery_time(skb, tstamp, mono_delivery_time);
> +                       skb_set_delivery_time(skb, tstamp, tstamp_type);
> 
> So maybe we need two variants, one that takes a tstamp_type and one
> that tames a clockid_t?
> 
> The first can be simple, not switch needed. Just apply the two stores.
I agree to what you are saying but clockid_t => points to int itself. 

For example :- 
		void qdisc_watchdog_init_clockid(struct qdisc_watchdog *wd, struct Qdisc *qdisc,
				 clockid_t clockid)

		qdisc_watchdog_init_clockid(wd, qdisc, CLOCK_MONOTONIC); => sch_api.c
	       qdisc_watchdog_init_clockid(&q->watchdog, sch, q->clockid); =>sch_etf.c (q->clockid is int)
	
But i can change it to two new APIs one which accepts only clock_id (with switch) and other accepts u8 to directly store whatever is given.