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Message-ID: <9a1f8011-2156-4855-8724-fea89d73df11@quicinc.com>
Date: Thu, 18 Apr 2024 12:58:00 -0700
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Subject: Re: [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to
 tstamp_type for scalabilty
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: <20240418004308.1009262-1-quic_abchauha@quicinc.com>
 <20240418004308.1009262-2-quic_abchauha@quicinc.com>
 <66216adc8677c_f648a294aa@willemb.c.googlers.com.notmuch>
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From: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>
In-Reply-To: <66216adc8677c_f648a294aa@willemb.c.googlers.com.notmuch>
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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@quicinc.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. 


> 
>