linux-kernel - Re: [RFC PATCH bpf-next v3 1/2] net: Rename mono_delivery_time to tstamp

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Date: Mon, 15 Apr 2024 14:26:10 -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 v3 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty



On 4/15/2024 2:22 PM, Willem de Bruijn wrote:
>>>>>>  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). 
> 
> Sorry, I got my defaults confused. If we maintain that a zero tstamp
> resets the type, then here should be no case with skb->tstamp 0 and
> skb->tstamp_type SKB_CLOCK_REAL (or SKB_CLOCK_TAI or whatever). I
> think it's preferable to make that obvious in the
> skb_set_delivery_time implementation, rather than depend on knowledge
> of its callers.

Noted!. I will do the same as part of the next patchset.