From: "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>
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>
Subject: Re: [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to tstamp_type for scalabilty
Date: Thu, 18 Apr 2024 13:51:43 -0700 [thread overview]
Message-ID: <f25fb07e-6885-447a-b91a-08efd5e01bcd@quicinc.com> (raw)
In-Reply-To: <6621874d772a9_fb2e029467@willemb.c.googlers.com.notmuch>
On 4/18/2024 1:49 PM, Willem de Bruijn wrote:
> Abhishek Chauhan (ABC) wrote:
>>
>>
>> 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@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.
>>>
>>> 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)
>
> My concern is more that we use CLOCK_MONOTONIC and SKB_CLOCK_MONO
> (and other clocks) interchangeably, without invariant checks to make
> sure that they map onto the same integer value.
Ah i see. I got it . I will make two APIs . Makes sense.
1. One can check for clockid => switch => set
2. One can set it directly.
next prev parent reply other threads:[~2024-04-18 20:52 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 0:43 [RFC PATCH bpf-next v4 0/2] Replace mono_delivery_time with tstamp_type Abhishek Chauhan
2024-04-18 0:43 ` [RFC PATCH bpf-next v4 1/2] net: Rename mono_delivery_time to tstamp_type for scalabilty Abhishek Chauhan
2024-04-18 18:47 ` Willem de Bruijn
2024-04-18 19:58 ` Abhishek Chauhan (ABC)
2024-04-18 20:11 ` Willem de Bruijn
2024-04-18 20:38 ` Abhishek Chauhan (ABC)
2024-04-18 20:49 ` Willem de Bruijn
2024-04-18 20:51 ` Abhishek Chauhan (ABC) [this message]
2024-04-18 0:43 ` [RFC PATCH bpf-next v4 2/2] net: Add additional bit to support clockid_t timestamp type Abhishek Chauhan
2024-04-18 19:06 ` Willem de Bruijn
2024-04-18 20:10 ` Abhishek Chauhan (ABC)
2024-04-18 21:57 ` Martin KaFai Lau
2024-04-19 0:30 ` Abhishek Chauhan (ABC)
2024-04-20 1:13 ` Abhishek Chauhan (ABC)
2024-04-22 18:46 ` Martin KaFai Lau
2024-04-24 18:03 ` Abhishek Chauhan (ABC)
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