From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-x533.google.com (mail-ed1-x533.google.com [IPv6:2a00:1450:4864:20::533]) by mail.toke.dk (Postfix) with ESMTPS id E46969C2EBC for ; Thu, 17 Nov 2022 03:59:53 +0100 (CET) Authentication-Results: mail.toke.dk; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20210112 header.b=AtKQ17Ed Received: by mail-ed1-x533.google.com with SMTP id u24so624340edd.13 for ; Wed, 16 Nov 2022 18:59:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=BmM/Ghh+hGvrYtxBIgPpo6ykm/qf83AzcsRNoCXujhg=; b=AtKQ17Edr7peecYZxZUvanH8YWm4B5mMyZ5eu83IaN+nVats82tAYwm4f4uKwWOpqd LJkJ6y+Htu7gZSU06ipqgbP7TKV+vEZOURvvI+UG7bfVWMehBOzW8XXf1UUsathp8cMX s6+k+F94uYDj13xDeY5ZfIbCAVxA1SFVD6meV3S1f0gyod0NTYvBrOKXs4MZUqOT1aMb sXrrlhUq/xFZEF7dUrEMpfJ8xCc3MHNPfGTsAzWciQXnKqX1OjNACZUs/ZbDWYhQTxCV D1tXesJpnDA+02J4swpjwNPj4heuPLFQHOCS80xmkg9IS4iUNOnBUSVGcjRUpd87ZMFD +LKg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=BmM/Ghh+hGvrYtxBIgPpo6ykm/qf83AzcsRNoCXujhg=; b=ses7Fg4YMedI6e8DXPSs88e5yRqt/cb9JUGYDtCWfLh/gXVLgFQzUxFAATLtYODJ9K 1w6H8z+BYposA6Iy9Ly63SRMBOO/74ShhHKnpX2dn5kQinAIFpCIYiZIA4ZbkyZChk56 NLJalR1VDQOcZ7m0tdHSr7AxUxImvrz9z0Sc2jc1f20RfL4gLCGyoIfSt/3rT9eowvCw yI4xok+7sWjGnkeiYPfRPXzfxSI3BCbGyqkqB/0XQzSS2hB2TJe4il5lHcoGN9TsiTE5 SzsZ/6D0acceZAxbV9iR5RubN2pPVNX7WgpF1qsCq8iFMyHzrj4dfl1FHOyWhjstWtet /f5Q== X-Gm-Message-State: ANoB5pnYcGqYNutfGxxEAP/XWTFjH/cSbXUfUxjNAL4Z3as/KnKbGNrs CZLetvINQB//8rX5iLzF1mtQUC7xu1ZGaJCFNGI= X-Google-Smtp-Source: AA0mqf7GHurn3nrqQassjpbWRDTwfsuweHWIQQ2IxehRveDcfYYrQ7DO3YDdcuVNoiBU6ZdkVH4KKzuPEuyRbDt62Rw= X-Received: by 2002:aa7:d604:0:b0:461:d726:438f with SMTP id c4-20020aa7d604000000b00461d726438fmr461314edr.333.1668653991978; Wed, 16 Nov 2022 18:59:51 -0800 (PST) MIME-Version: 1.0 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> In-Reply-To: From: Alexei Starovoitov Date: Wed, 16 Nov 2022 18:59:40 -0800 Message-ID: To: Stanislav Fomichev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: B24HEO3BB6DPFAKFHTWFT3V4OBEXLM3V X-Message-ID-Hash: B24HEO3BB6DPFAKFHTWFT3V4OBEXLM3V X-MailFrom: alexei.starovoitov@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: John Fastabend , =?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: 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 wro= te: > > > > > > 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_patch *patch) > > > > > > > >>>>>>> +{ > > > > > > > >>>>>>> + if (func_id =3D=3D xdp_metadata_kfunc_id(XDP_ME= TADATA_KFUNC_RX_TIMESTAMP_SUPPORTED)) { > > > > > > > >>>>>>> + /* return true; */ > > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_MOV64_IMM(B= PF_REG_0, 1)); > > > > > > > >>>>>>> + } else if (func_id =3D=3D xdp_metadata_kfunc_id= (XDP_METADATA_KFUNC_RX_TIMESTAMP)) { > > > > > > > >>>>>>> + /* return ktime_get_mono_fast_ns(); */ > > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_EMIT_CALL(k= time_get_mono_fast_ns)); > > > > > > > >>>>>>> + } > > > > > > > >>>>>>> +} > > > > > > > >>>>>> > > > > > > > >>>>>> So these look reasonable enough, but would be good to = see some examples > > > > > > > >>>>>> of kfunc implementations that don't just BPF_CALL to a= kernel function > > > > > > > >>>>>> (with those helper wrappers we were discussing before)= . > > > > > > > >>>>> > > > > > > > >>>>> Let's maybe add them if/when needed as we add more meta= data support? > > > > > > > >>>>> xdp_metadata_export_to_skb has an example, and rfc 1/2 = have more > > > > > > > >>>>> examples, so it shouldn't be a problem to resurrect the= m back at some > > > > > > > >>>>> point? > > > > > > > >>>> > > > > > > > >>>> Well, the reason I asked for them is that I think having= to maintain the > > > > > > > >>>> BPF code generation in the drivers is probably the bigge= st drawback of > > > > > > > >>>> the kfunc approach, so it would be good to be relatively= sure that we > > > > > > > >>>> can manage that complexity (via helpers) before we commi= t 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 back without = any real users? > > > > > > > >>> Because I had to remove my veth tstamp accessors due to J= ohn/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 "would be goo= d to see some > > > > > > > >> examples of kfunc implementations that don't just BPF_CALL= to a kernel > > > > > > > >> function"? In this case do you mean BPF code directly with= out the call? > > > > > > > >> > > > > > > > >> Early on I thought we should just expose the rx_descriptor= which would > > > > > > > >> be roughly the same right? (difference being code embedded= in driver vs > > > > > > > >> a lib) Trouble I ran into is driver code using seqlock_t a= nd mutexs > > > > > > > >> which wasn't as straight forward as the simpler just read = it from > > > > > > > >> the descriptor. For example in mlx getting the ts 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_cq= e *)cqe; > > > > > > > >> > > > > > > > >> lo =3D (u64)be16_to_cpu(ts_cqe->timestamp_lo); > > > > > > > >> hi =3D ((u64)be32_to_cpu(ts_cqe->timestamp_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_hwtstamps *= hwts, > > > > > > > >> u64 timestamp) > > > > > > > >> { > > > > > > > >> unsigned int seq; > > > > > > > >> u64 nsec; > > > > > > > >> > > > > > > > >> do { > > > > > > > >> seq =3D read_seqbegin(&mdev->clock_lock); > > > > > > > >> nsec =3D timecounter_cyc2time(&mdev->cloc= k, timestamp); > > > > > > > >> } while (read_seqretry(&mdev->clock_lock, seq)); > > > > > > > >> > > > > > > > >> memset(hwts, 0, sizeof(struct skb_shared_hwtstamp= s)); > > > > > > > >> hwts->hwtstamp =3D ns_to_ktime(nsec); > > > > > > > >> } > > > > > > > >> > > > > > > > >> I think the nsec is what you really want. > > > > > > > >> > > > > > > > >> With all the drivers doing slightly different ops we would= have > > > > > > > >> to create read_seqbegin, read_seqretry, mutex_lock, ... to= get > > > > > > > >> at least the mlx and ice drivers it looks like we would ne= ed some > > > > > > > >> more BPF primitives/helpers. Looks like some more work is = needed > > > > > > > >> on ice driver though to get rx tstamps on all packets. > > > > > > > >> > > > > > > > >> Anyways this convinced me real devices will probably use B= PF_CALL > > > > > > > >> and not BPF insns directly. > > > > > > > > > > > > > > > > Some of the mlx5 path looks like this: > > > > > > > > > > > > > > > > #define REAL_TIME_TO_NS(hi, low) (((u64)hi) * NSEC_PER_SEC = + ((u64)low)) > > > > > > > > > > > > > > > > static inline ktime_t mlx5_real_time_cyc2time(struct mlx5_c= lock *clock, > > > > > > > > u64 timestam= p) > > > > > > > > { > > > > > > > > u64 time =3D REAL_TIME_TO_NS(timestamp >> 32, time= stamp & 0xFFFFFFFF); > > > > > > > > > > > > > > > > return ns_to_ktime(time); > > > > > > > > } > > > > > > > > > > > > > > > > If some hints are harder to get, then just doing a kfunc ca= ll 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 performan= ce 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 benchm= ark this > > > > > > > series against Jesper's; which I think we should definitely b= e doing > > > > > > > before merging this. > > > > > > > > > > > > Good point I got sort of singularly focused on timestamp becaus= e 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 inline-able) o= n the > > > > > rx side for a v2. > > > > > > > > If you go with in-kernel BPF kfunc approach (vs user space side) I = think > > > > you also need to add CO-RE to be friendly for driver developers? Ot= herwise > > > > they have to keep that read in sync with the descriptors? Also need= to > > > > handle versioning of descriptors where depending on specific option= s > > > > and firmware and chip being enabled the descriptor might be moving > > > > around. Of course can push this all to developer, but seems 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_desc->csum an= d > > > > expect CO-RE sorts it out based on currently running btf_id of the > > > > descriptor. If you go through normal path you get this for free of > > > > course. > > > > > > Doesn't look like the descriptors are as nice as you're trying to > > > paint them (with clear hash/csum fields) :-) So not sure how 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 unlucky with > > > mlx4? > > > > Which part are you talking about ? > > hw_checksum =3D csum_unfold((__force __sum16)cqe->checksum); > > is trivial enough for bpf prog to do if it has access to 'cqe' pointer > > which is what John is proposing (I think). > > I'm talking about mlx4_en_process_rx_cq, the caller of that check_csum. > In particular: if (likely(dev->features & NETIF_F_RXCSUM)) branch > I'm assuming we want to have hash_type available to the progs? > > But also, check_csum handles other corner cases: > - short_frame: we simply force all those small frames to skip checksum co= mplete > - get_fixed_ipv6_csum: In IPv6 packets, hw_checksum lacks 6 bytes from > IPv6 header > - get_fixed_ipv4_csum: Although the stack expects checksum which > doesn't include the pseudo header, the HW adds it Of course, but kfunc won't be doing them either. We're talking XDP fast path. The mlx4 hw is old and incapable. No amount of sw can help. > So it doesn't look like we can just unconditionally use cqe->checksum? > The driver does a lot of massaging around that field to make it > palatable. Of course we can. cqe->checksum is still usable. the bpf prog would need to know what it's reading. There should be no attempt to present a unified state of hw bits. That's what skb is for. XDP layer should not hide such hw details. Otherwise it will become a mini skb layer with all that overhead.