From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-x22a.google.com (mail-oi1-x22a.google.com [IPv6:2607:f8b0:4864:20::22a]) by mail.toke.dk (Postfix) with ESMTPS id 503D09C2EA4 for ; Thu, 17 Nov 2022 03:53:50 +0100 (CET) Authentication-Results: mail.toke.dk; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20210112 header.b=nv4UF/qg Received: by mail-oi1-x22a.google.com with SMTP id n205so535759oib.1 for ; Wed, 16 Nov 2022 18:53:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.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=N1WiWI19YoHyMhnLxSGvNdwVK87PQdtocGJoZYJrP8w=; b=nv4UF/qgrmqTzrar//wrdDt98dkonq6j8OlyfQJnrhLCbJR3RKkUefl7U8OFl16bRf nVZYl7gJwq03vaxFt5e3hjlWUbq8IiP174cBTMMlf8YkdaPuW0UMLesal+1z3gTLtbzD LAfKx6pj4HeQjkMMZsisFFtRTMB1/7AwQl29BCyzHjLaPWDwak1nsfy7FhqMf0vOvmI4 BSSZzBOdjIDFmoZCxWuxQKaCJwvooSCWnxnB0hWNwQl7TVfgnLy4lLq4VFFMs9lhLYvM n1m9kBPx4sxdyh0qTfRSDDHSD8wCiNm2tcd0YtT3wKtcOPLuYcSUp2SmZsDA1gwRNHsk CF1A== 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=N1WiWI19YoHyMhnLxSGvNdwVK87PQdtocGJoZYJrP8w=; b=kXtr7X/aiaVH0E/C8DPYG1KYW81YmMOEkf6jaH4/F72Wi7yUu3+IkyzIKpsCPDfZU6 2mfR68wSawa2PzOHgyXpNkq1NFO+Jy+dXHujovPU1/5ETvkTQEQCgvW+8y+lu/VLhKJI RA8PCBljQ4Pa393oaXNXlCr7iirD94gN9ax5DtYm8pVzgGD8ob+/YKO8tmGc54EujbMu VYNptZkpcsUcVA0PInY1FE1o71w6MVnSSkdd4SMeez2S4oBZK65sk0zNF9lemGW1iqfD DP3rwqdBrBHXdHoHczhO2PpyqB30Quk413omJ6MhKoolhDjm1K2QDkU3+HRrJd0FtGss 7v7g== X-Gm-Message-State: ANoB5pkpbt+dScp8Rh9lzRr1QpKuZ7VVOrKqgBgPdu71IzCTYVi63sFz W+KUDZ5mVCQOYuD7oBdp0mEDB5DaV/o03tvpvGjm+A== X-Google-Smtp-Source: AA0mqf6znsj3SSKwj4NdK7G3r/Lu8/Wr7RkL1YYIscb75J6M13IY6mdHJYJBFwzG6Jzcnu1M1iRbHHPLARNf5ycfK5M= X-Received: by 2002:aca:1802:0:b0:359:e812:69ee with SMTP id h2-20020aca1802000000b00359e81269eemr3215524oih.125.1668653627378; Wed, 16 Nov 2022 18:53:47 -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: Stanislav Fomichev Date: Wed, 16 Nov 2022 18:53:36 -0800 Message-ID: To: Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: L5YSV4ZRHT6FE7EH2J3J76C6TGEJZRQA X-Message-ID-Hash: L5YSV4ZRHT6FE7EH2J3J76C6TGEJZRQA X-MailFrom: sdf@google.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 6:17 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 *p= rog, u32 func_id, > > > > > > >>>>>>> + struct bpf_patch *patch) > > > > > > >>>>>>> +{ > > > > > > >>>>>>> + if (func_id =3D=3D xdp_metadata_kfunc_id(XDP_META= DATA_KFUNC_RX_TIMESTAMP_SUPPORTED)) { > > > > > > >>>>>>> + /* return true; */ > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_MOV64_IMM(BPF= _REG_0, 1)); > > > > > > >>>>>>> + } else if (func_id =3D=3D xdp_metadata_kfunc_id(X= DP_METADATA_KFUNC_RX_TIMESTAMP)) { > > > > > > >>>>>>> + /* return ktime_get_mono_fast_ns(); */ > > > > > > >>>>>>> + bpf_patch_append(patch, BPF_EMIT_CALL(kti= me_get_mono_fast_ns)); > > > > > > >>>>>>> + } > > > > > > >>>>>>> +} > > > > > > >>>>>> > > > > > > >>>>>> So these look reasonable enough, but would be good to se= e some examples > > > > > > >>>>>> of kfunc implementations that don't just BPF_CALL to a k= ernel function > > > > > > >>>>>> (with those helper wrappers we were discussing before). > > > > > > >>>>> > > > > > > >>>>> Let's maybe add them if/when needed as we add more metada= ta support? > > > > > > >>>>> xdp_metadata_export_to_skb has an example, and rfc 1/2 ha= ve more > > > > > > >>>>> examples, so it shouldn't be a problem to resurrect them = back at some > > > > > > >>>>> point? > > > > > > >>>> > > > > > > >>>> Well, the reason I asked for them is that I think having t= o 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 s= ure that we > > > > > > >>>> can manage that complexity (via helpers) before we commit = to this :) > > > > > > >>> > > > > > > >>> Right, and I've added a bunch of examples in v2 rfc so we c= an judge > > > > > > >>> whether that complexity is manageable or not :-) > > > > > > >>> Do you want me to add those wrappers you've back without an= y real users? > > > > > > >>> Because I had to remove my veth tstamp accessors due to Joh= n/Jesper > > > > > > >>> objections; I can maybe bring some of this back gated by so= me > > > > > > >>> static_branch to avoid the fastpath cost? > > > > > > >> > > > > > > >> I missed the context a bit what did you mean "would be good = to see some > > > > > > >> examples of kfunc implementations that don't just BPF_CALL t= o a kernel > > > > > > >> function"? In this case do you mean BPF code directly withou= t the call? > > > > > > >> > > > > > > >> Early on I thought we should just expose the rx_descriptor w= hich would > > > > > > >> be roughly the same right? (difference being code embedded i= n driver vs > > > > > > >> a lib) Trouble I ran into is driver code using seqlock_t and= 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 e= asy 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->timestamp_lo); > > > > > > >> hi =3D ((u64)be32_to_cpu(ts_cqe->timestamp_hi) + !l= o) << 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 *hw= ts, > > > > > > >> u64 timestamp) > > > > > > >> { > > > > > > >> unsigned int seq; > > > > > > >> u64 nsec; > > > > > > >> > > > > > > >> do { > > > > > > >> seq =3D read_seqbegin(&mdev->clock_lock); > > > > > > >> nsec =3D timecounter_cyc2time(&mdev->clock,= timestamp); > > > > > > >> } while (read_seqretry(&mdev->clock_lock, seq)); > > > > > > >> > > > > > > >> memset(hwts, 0, sizeof(struct skb_shared_hwtstamps)= ); > > > > > > >> 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 h= ave > > > > > > >> to create read_seqbegin, read_seqretry, mutex_lock, ... to g= et > > > > > > >> at least the mlx and ice drivers it looks like we would need= some > > > > > > >> more BPF primitives/helpers. Looks like some more work is ne= eded > > > > > > >> on ice driver though to get rx tstamps on all packets. > > > > > > >> > > > > > > >> Anyways this convinced me real devices will probably 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) * NSEC_PER_SEC + = ((u64)low)) > > > > > > > > > > > > > > static inline ktime_t mlx5_real_time_cyc2time(struct mlx5_clo= ck *clock, > > > > > > > u64 timestamp) > > > > > > > { > > > > > > > u64 time =3D REAL_TIME_TO_NS(timestamp >> 32, timest= amp & 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 fi= eld in > > > > > > the metadata, that will end up having a significant performance= impact > > > > > > on the XDP data path (thinking mostly about the skb metadata ca= se 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 benchmar= k this > > > > > > series against Jesper's; which I think we should definitely be = doing > > > > > > before merging this. > > > > > > > > > > Good point I got sort of singularly focused on timestamp 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 inline-able) on = the > > > > rx side for a v2. > > > > > > If you go with in-kernel BPF kfunc approach (vs user space side) I th= ink > > > you also need to add CO-RE to be friendly for driver developers? Othe= rwise > > > they have to keep that read in sync with the descriptors? Also need t= o > > > handle versioning of descriptors where depending on specific options > > > 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 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 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 comp= lete - 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 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.