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Thu, 17 Nov 2022 11:47:56 -0800 (PST) Date: Thu, 17 Nov 2022 11:47:54 -0800 From: John Fastabend To: Stanislav Fomichev , John Fastabend Message-ID: <63768feaf1324_4101208cf@john.notmuch> In-Reply-To: References: <20221115030210.3159213-1-sdf@google.com> <20221115030210.3159213-6-sdf@google.com> <87h6z0i449.fsf@toke.dk> <8735ajet05.fsf@toke.dk> <6374854883b22_5d64b208e3@john.notmuch> <34f89a95-a79e-751c-fdd2-93889420bf96@linux.dev> <878rkbjjnp.fsf@toke.dk> <6375340a6c284_66f16208aa@john.notmuch> <637576962dada_8cd03208b0@john.notmuch> <6375dad15f11f_9c882208b5@john.notmuch> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Message-ID-Hash: 733NE5TENW2XKDPMBYL7HBVFL3ZXSZ5G X-Message-ID-Hash: 733NE5TENW2XKDPMBYL7HBVFL3ZXSZ5G X-MailFrom: john.fastabend@gmail.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Alexei Starovoitov , =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Martin KaFai Lau , bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , David Ahern , Jakub Kicinski , Willem de Bruijn , Jesper Dangaard Brouer , Anatoly Burakov , Alexander Lobakin , Magnus Karlsson , Maryam Tahhan , xdp-hints@xdp-project.net, Network Development X-Mailman-Version: 3.3.6 Precedence: list Subject: [xdp-hints] Re: [PATCH bpf-next 05/11] veth: Support rx timestamp metadata for xdp List-Id: XDP hardware hints design discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Stanislav Fomichev wrote: > On Wed, Nov 16, 2022 at 10:55 PM John Fastabend > wrote: > > > > Stanislav Fomichev wrote: > > > On Wed, Nov 16, 2022 at 6:59 PM Alexei Starovoitov > > > wrote: > > > > > > > > On Wed, Nov 16, 2022 at 6:53 PM Stanislav Fomichev wrote: > > > > > > > > > > On Wed, Nov 16, 2022 at 6:17 PM Alexei Starovoitov > > > > > wrote: > > > > > > > > > > > > On Wed, Nov 16, 2022 at 4:19 PM Stanislav Fomichev wrote: > > > > > > > > > > > > > > On Wed, Nov 16, 2022 at 3:47 PM John Fastabend wrote: > > > > > > > > > > > > > > > > Stanislav Fomichev wrote: > > > > > > > > > On Wed, Nov 16, 2022 at 11:03 AM John Fastabend > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > Toke H=C3=B8iland-J=C3=B8rgensen wrote: > > > > > > > > > > > Martin KaFai Lau writes: > > > > > > > > > > > > > > > > > > > > > > > On 11/15/22 10:38 PM, John Fastabend wrote: > > > > > > > > > > > >>>>>>> +static void veth_unroll_kfunc(const struct= bpf_prog *prog, u32 func_id, > > > > > > > > > > > >>>>>>> + struct bpf_patc= h *patch) > > > > > > > > > > > >>>>>>> +{ > > > > > > > > > > > >>>>>>> + if (func_id =3D=3D xdp_metadata_kfunc= _id(XDP_METADATA_KFUNC_RX_TIMESTAMP_SUPPORTED)) { > > > > > > > > > > > >>>>>>> + /* return true; */ > > > > > > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_M= OV64_IMM(BPF_REG_0, 1)); > > > > > > > > > > > >>>>>>> + } else if (func_id =3D=3D xdp_metadat= a_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP)) { > > > > > > > > > > > >>>>>>> + /* return ktime_get_mono_fast= _ns(); */ > > > > > > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_E= MIT_CALL(ktime_get_mono_fast_ns)); > > > > > > > > > > > >>>>>>> + } > > > > > > > > > > > >>>>>>> +} > > > > > > > > > > > >>>>>> > > > > > > > > > > > >>>>>> So these look reasonable enough, but would b= e good to see some examples > > > > > > > > > > > >>>>>> of kfunc implementations that don't just BPF= _CALL to a kernel function > > > > > > > > > > > >>>>>> (with those helper wrappers we were discussi= ng before). > > > > > > > > > > > >>>>> > > > > > > > > > > > >>>>> Let's maybe add them if/when needed as we add= more metadata support? > > > > > > > > > > > >>>>> xdp_metadata_export_to_skb has an example, an= d rfc 1/2 have more > > > > > > > > > > > >>>>> examples, so it shouldn't be a problem to res= urrect them back at some > > > > > > > > > > > >>>>> point? > > > > > > > > > > > >>>> > > > > > > > > > > > >>>> Well, the reason I asked for them is that I th= ink having to maintain the > > > > > > > > > > > >>>> BPF code generation in the drivers is probably= the biggest drawback of > > > > > > > > > > > >>>> the kfunc approach, so it would be good to be = relatively sure that we > > > > > > > > > > > >>>> can manage that complexity (via helpers) befor= e we commit to this :) > > > > > > > > > > > >>> > > > > > > > > > > > >>> Right, and I've added a bunch of examples in v2= rfc so we can judge > > > > > > > > > > > >>> whether that complexity is manageable or not :-= ) > > > > > > > > > > > >>> Do you want me to add those wrappers you've bac= k without any real users? > > > > > > > > > > > >>> Because I had to remove my veth tstamp accessor= s due to John/Jesper > > > > > > > > > > > >>> objections; I can maybe bring some of this back= gated by some > > > > > > > > > > > >>> static_branch to avoid the fastpath cost? > > > > > > > > > > > >> > > > > > > > > > > > >> I missed the context a bit what did you mean "wo= uld be good to see some > > > > > > > > > > > >> examples of kfunc implementations that don't jus= t BPF_CALL to a kernel > > > > > > > > > > > >> function"? In this case do you mean BPF code dir= ectly without the call? > > > > > > > > > > > >> > > > > > > > > > > > >> Early on I thought we should just expose the rx_= descriptor which would > > > > > > > > > > > >> be roughly the same right? (difference being cod= e embedded in driver vs > > > > > > > > > > > >> a lib) Trouble I ran into is driver code using s= eqlock_t and mutexs > > > > > > > > > > > >> which wasn't as straight forward as the simpler = just read it from > > > > > > > > > > > >> the descriptor. For example in mlx getting the t= s would be easy from > > > > > > > > > > > >> BPF with the mlx4_cqe struct exposed > > > > > > > > > > > >> > > > > > > > > > > > >> u64 mlx4_en_get_cqe_ts(struct mlx4_cqe *cqe) > > > > > > > > > > > >> { > > > > > > > > > > > >> u64 hi, lo; > > > > > > > > > > > >> struct mlx4_ts_cqe *ts_cqe =3D (struct = mlx4_ts_cqe *)cqe; > > > > > > > > > > > >> > > > > > > > > > > > >> lo =3D (u64)be16_to_cpu(ts_cqe->timesta= mp_lo); > > > > > > > > > > > >> hi =3D ((u64)be32_to_cpu(ts_cqe->timest= amp_hi) + !lo) << 16; > > > > > > > > > > > >> > > > > > > > > > > > >> return hi | lo; > > > > > > > > > > > >> } > > > > > > > > > > > >> > > > > > > > > > > > >> but converting that to nsec is a bit annoying, > > > > > > > > > > > >> > > > > > > > > > > > >> void mlx4_en_fill_hwtstamps(struct mlx4_en_dev *= mdev, > > > > > > > > > > > >> struct skb_shared_h= wtstamps *hwts, > > > > > > > > > > > >> u64 timestamp) > > > > > > > > > > > >> { > > > > > > > > > > > >> unsigned int seq; > > > > > > > > > > > >> u64 nsec; > > > > > > > > > > > >> > > > > > > > > > > > >> do { > > > > > > > > > > > >> seq =3D read_seqbegin(&mdev->cl= ock_lock); > > > > > > > > > > > >> nsec =3D timecounter_cyc2time(&= mdev->clock, timestamp); > > > > > > > > > > > >> } while (read_seqretry(&mdev->clock_loc= k, seq)); > > > > > > > > > > > >> > > > > > > > > > > > >> memset(hwts, 0, sizeof(struct skb_share= d_hwtstamps)); > > > > > > > > > > > >> hwts->hwtstamp =3D ns_to_ktime(nsec); > > > > > > > > > > > >> } > > > > > > > > > > > >> > > > > > > > > > > > >> I think the nsec is what you really want. > > > > > > > > > > > >> > > > > > > > > > > > >> With all the drivers doing slightly different op= s we would have > > > > > > > > > > > >> to create read_seqbegin, read_seqretry, mutex_lo= ck, ... to get > > > > > > > > > > > >> at least the mlx and ice drivers it looks like w= e would need some > > > > > > > > > > > >> more BPF primitives/helpers. Looks like some mor= e work is needed > > > > > > > > > > > >> on ice driver though to get rx tstamps on all pa= ckets. > > > > > > > > > > > >> > > > > > > > > > > > >> Anyways this convinced me real devices will prob= ably use BPF_CALL > > > > > > > > > > > >> and not BPF insns directly. > > > > > > > > > > > > > > > > > > > > > > > > Some of the mlx5 path looks like this: > > > > > > > > > > > > > > > > > > > > > > > > #define REAL_TIME_TO_NS(hi, low) (((u64)hi) * NSE= C_PER_SEC + ((u64)low)) > > > > > > > > > > > > > > > > > > > > > > > > static inline ktime_t mlx5_real_time_cyc2time(str= uct mlx5_clock *clock, > > > > > > > > > > > > u6= 4 timestamp) > > > > > > > > > > > > { > > > > > > > > > > > > u64 time =3D REAL_TIME_TO_NS(timestamp >= > 32, timestamp & 0xFFFFFFFF); > > > > > > > > > > > > > > > > > > > > > > > > return ns_to_ktime(time); > > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > > > If some hints are harder to get, then just doing = a kfunc call is better. > > > > > > > > > > > > > > > > > > > > > > Sure, but if we end up having a full function call = for every field in > > > > > > > > > > > the metadata, that will end up having a significant= performance impact > > > > > > > > > > > on the XDP data path (thinking mostly about the skb= metadata case here, > > > > > > > > > > > which will collect several bits of metadata). > > > > > > > > > > > > > > > > > > > > > > > csum may have a better chance to inline? > > > > > > > > > > > > > > > > > > > > > > Yup, I agree. Including that also makes it possible= to benchmark this > > > > > > > > > > > series against Jesper's; which I think we should de= finitely be doing > > > > > > > > > > > before merging this. > > > > > > > > > > > > > > > > > > > > Good point I got sort of singularly focused on timest= amp because I have > > > > > > > > > > a use case for it now. > > > > > > > > > > > > > > > > > > > > Also hash is often sitting in the rx descriptor. > > > > > > > > > > > > > > > > > > Ack, let me try to add something else (that's more inli= ne-able) on the > > > > > > > > > rx side for a v2. > > > > > > > > > > > > > > > > If you go with in-kernel BPF kfunc approach (vs user spac= e side) I think > > > > > > > > you also need to add CO-RE to be friendly for driver deve= lopers? Otherwise > > > > > > > > they have to keep that read in sync with the descriptors?= Also need to > > > > > > > > handle versioning of descriptors where depending on speci= fic options > > > > > > > > and firmware and chip being enabled the descriptor might = be moving > > > > > > > > around. Of course can push this all to developer, but see= ms not so > > > > > > > > nice when we have the machinery to do this and we handle = it for all > > > > > > > > other structures. > > > > > > > > > > > > > > > > With CO-RE you can simply do the rx_desc->hash and rx_des= c->csum and > > > > > > > > expect CO-RE sorts it out based on currently running btf_= id of the > > > > > > > > descriptor. If you go through normal path you get this fo= r free of > > > > > > > > course. > > > > > > > > > > > > > > Doesn't look like the descriptors are as nice as you're try= ing to > > > > > > > paint them (with clear hash/csum fields) :-) So not sure ho= w much > > > > > > > CO-RE would help. > > > > > > > At least looking at mlx4 rx_csum, the driver consults three= different > > > > > > > sets of flags to figure out the hash_type. Or am I just unl= ucky with > > > > > > > mlx4? > > > > > > > > > > > > Which part are you talking about ? > > > > > > hw_checksum =3D csum_unfold((__force __sum16)cqe->che= cksum); > > > > > > is trivial enough for bpf prog to do if it has access to 'cqe= ' pointer > > > > > > which is what John is proposing (I think). > > > > Yeah this is what I've been considering. If you just get the 'cqe' po= inter > > walking the check_sum and rxhash should be straightforward. > > > > There seems to be a real difference between timestamps and most other= > > fields IMO. Timestamps require some extra logic to turn into ns when > > using the NIC hw clock. And the hw clock requires some coordination t= o > > keep in sync and stop from overflowing and may be done through other > > protocols like PTP in my use case. In some cases I think the clock is= > > also shared amongst multiple phys. Seems mlx has a seqlock_t to prote= ct > > it and I'm less sure about this but seems intel nic maybe has a sideb= and > > control channel. > > > > Then there is everything else that I can think up that is per packet = data > > and requires no coordination with the driver. Its just reading fields= in > > the completion queue. This would be the csum, check_sum, vlan_header = and > > so on. Sure we could kfunc each one of those things, but could also j= ust > > write that directly in BPF and remove some abstractions and kernel > > dependency by doing it directly in the BPF program. If you like that > > abstraction seems to be the point of contention my opinion is the cos= t > > of kernel depency is high and I can abstract it with a user library > > anyways so burying it in the kernel only causes me support issues and= > > backwards compat problems. > > > > Hopefully, my position is more clear. > = > Yeah, I see your point, I'm somewhat in the same position here wrt to > legacy kernels :-) > Exposing raw descriptors seems fine, but imo it shouldn't be the goto > mechanism for the metadata; but rather as a fallback whenever the > driver implementation is missing/buggy. Unless, as you mention below, > there are some libraries in the future to abstract that. > But at least it seems that we agree that there needs to be some other > non-raw-descriptor way to access spinlocked things like the timestamp? > = Yeah for timestamps I think a kfunc to either get the timestamp or could also be done with a kfunc to read hw clock. But either way seems hard to do that in BPF code directly so kfunc feels right to me here. By the way I think if you have the completion queue (rx descriptor) in the xdp_buff and we use Yonghong's patch to cast the ctx as a BTF type then we should be able to also directly read all the fields. I see you noted this in the response to Alexei so lets see what he thinks.=