Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit for userspace tstamp packets

[Martin KaFai Lau]

On 3/19/24 11:22 PM, Abhishek Chauhan (ABC) wrote:
> On 3/18/2024 12:02 PM, Abhishek Chauhan (ABC) wrote:
> > On 3/14/2024 3:29 PM, Abhishek Chauhan (ABC) wrote:
> > > On 3/14/2024 2:48 PM, Martin KaFai Lau wrote:
> > > > On 3/14/24 1:53 PM, Abhishek Chauhan (ABC) wrote:
> > > > > > > The bpf_convert_tstamp_{read,write} and the helper bpf_skb_set_tstamp need to be
> > > > > > > changed to handle the new "user_delivery_time" bit anyway, e.g.
> > > > > > > bpf_skb_set_tstamp(BPF_SKB_TSTAMP_DELIVERY_MONO) needs to clear the
> > > > > > > "user_delivery_time" bit.
> > > > > > >
> > > > > > > I think the "struct inet_frag_queue" also needs a new "user_delivery_time"
> > > > > > > field. "mono_delivery_time" is already in there.
> > > >
> > > > [ ... ]
> >
> > Martin, Do we really need to add user_delivery_time as part of inet_frag_queue struct? I was wondering why is this required since we are using tstamp_type:2 to
> > distinguish between timestamp anyway .
> >
> > Let me know what you think ?
> >
> > > > I would think the first step is to revert this patch. I don't think much of the current patch can be reused.
> > > >
> > > > > 1. I will raise one patch to introduce rename mono_delivery_time to
> > > > > tstamp_type
> > > >
> > > > Right, I expect something like this:
> > > >
> > > > struct sk_buff {
> > > >          /* ... */
> > > > -            __u8                    mono_delivery_time:1;
> > > > +        __u8            tstamp_type:1;
> > > >          /* ... */
> > > > };
> > >
> > > Okay ,This should be straight-forward.
> > >
> > > > > 2. I will introduce setting of userspace timestamp type as the second bit
> > > > > whem transmit_time is set.
> > > >
> > > > I expect the second patch should be introducing the enum first
> > > >
> > > > enum skb_tstamp_type {
> > > >      SKB_TSTAMP_TYPE_RX_REAL = 0, /* A RX (receive) time in real */
> > > >      SKB_TSTAMP_TYPE_TX_MONO = 1, /* A TX (delivery) time in mono */
> > > > };
> > > >
> > > > and start doing "skb->tstamp_type = SKB_TSTAMP_TYPE_TX_MONO;" instead of
> > > > "skb->tstamp_type = 1;"
> > > >
> > > > and the same for "skb->tstamp_type = SKB_TSTAMP_TYPE_RX_REAL;" instead of
> > > > "skb->tstamp_type = 0;"
> > > >
> > > >
> > > > This one I am not sure but probably need to change the skb_set_delivery_time() function signature also:
> > > >
> > > > static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
> > > > -                                        bool mono)
> > > > +                     enum skb_tstamp_type tstamp_type)
> > > This should be straight-forward as well
> > >
> > > > The third patch is to change tstamp_type from 1 bit to 2 bits and add SKB_TSTAMP_TYPE_TX_USER.
> > > >
> > > > struct sk_buff {
> > > >          /* ... */
> > > > -        __u8            tstamp_type:1;
> > > > +        __u8            tstamp_type:2;
> > > >          /* ... */
> > > > };
> > > >
> > > > enum skb_tstamp_type {
> > > >      SKB_TSTAMP_TYPE_RX_REAL = 0,    /* A RX (receive) time in real */
> > > >      SKB_TSTAMP_TYPE_TX_MONO = 1,    /* A TX (delivery) time in mono */
> > > > +    SKB_TSTAMP_TYPE_TX_USER = 2,    /* A TX (delivery) time and its clock
> > > >                       * is in skb->sk->sk_clockid.
> > > >                       */
> > > >                 
> > > > };
> > > >
> > > > This will shift a bit out of the byte where tstamp_type lives. It should be the "inner_protocol_type" bit by my hand count. Please check if it is directly used in bpf instruction (filter.c). As far as I look, it is not, so should be fine. Some details about bpf instruction accessible skb bit field here: https://lore.kernel.org/all/20230321014115.997841-1-kuba@xxxxxxxxxx/
> > > This is where i would need thorough reviews from you and Willem as my area of expertise is limited to part of network stack and BPF is not one of them.
> > > But i have plan on this and i know how to do it.
> > >
> > > Expect patches to be arriving to your inboxes next week, as we have a long weekend in Qualcomm
> > > Fingers crossed :)
> > >
> > > > > 3. This will be a first step to make the design scalable.
> > > > > 4. Tomorrow if we have more timestamp to support, upstream community has to do is
> > > > > update the enum and increase the bitfield from 2=>3 and so on.
> > > > >
> > > > > I need help from Martin to test the patch which renames the mono_delivery_time
> > > > > to tstamp_type (Which i feel should be straight forward as the value of the bit is 1)
> > > >
> > > > The bpf change is not a no-op rename of mono_delivery_time. It needs to take care of the new bit added to the tstamp_type. Please see the previous email (and I also left it in the beginning of this email).
> > > >
> > > > Thus, you need to compile the selftests/bpf/ and run it to verify the changes when handling the new bit. The Documentation/bpf/bpf_devel_QA.rst has the howto details. You probably only need the newer llvm (newer gcc should work also as bpf CI has been using it) and the newer pahole. I can definitely help if there is issue in running the test_progs in selftests/bpf or you have question on making the changes in filter.c. To run the test: "./test_progs -t tc_redirect/tc_redirect_dtime"
>
> Martin,
> I was able to compile test_progs and execute the above command mentioned by you . Does the output look okay for you ?
>
> [ 3076.040766] IPv6: ADDRCONF(NETDEV_CHANGE): veth_src_fwd: link becomes ready
> [ 3076.040809] IPv6: ADDRCONF(NETDEV_CHANGE): veth_src: link becomes ready
> [ 3076.072844] IPv6: ADDRCONF(NETDEV_CHANGE): veth_dst: link becomes ready
> [ 3076.072880] IPv6: ADDRCONF(NETDEV_CHANGE): veth_dst_fwd: link becomes ready
> #214/5   tc_redirect/tc_redirect_dtime:OK
> #214     tc_redirect:OK

lgtm. thanks.