From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oa1-x2b.google.com (mail-oa1-x2b.google.com [IPv6:2001:4860:4864:20::2b]) by mail.toke.dk (Postfix) with ESMTPS id 6CC779C2E0C for ; Thu, 17 Nov 2022 01:19:28 +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=QMh1jxbm Received: by mail-oa1-x2b.google.com with SMTP id 586e51a60fabf-13bd19c3b68so402014fac.7 for ; Wed, 16 Nov 2022 16:19:27 -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=9TyfACSP5CqF7d2bU0CR499dqnJ0ios8jlp6awifBbA=; b=QMh1jxbmXAlGrPRYJzRrdSZvo8/qsta5NZeB7ogVkdggT3zXN8WtZwiCmncdXyNXv9 fT7T+cz1CuHRmrpJIT4FCo8nvMfcNXgVMewB7wKwd0jlXSlqQWB5KdEz+/zjwpPvYQ3t 4o4ZkCjVlTvmlCeSJl2XybJ82DnRpSx/aJXzWsx4NwLxbtpAR2TQjbqDqnhqGvHFRqdJ WxBCSMauFzqZ5kjUUhRDwJmIb4peATuiAjpNlfoud6E9dqnj4i6dPihLLZbjTH67SpMI golmjyGFBaJN7oDRVDUt4eGRj9lITu40jL6k8HKy1JPPGTfYT/J1CevDPQcqLoiz3haj A8Wg== 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=9TyfACSP5CqF7d2bU0CR499dqnJ0ios8jlp6awifBbA=; b=C+yAzBnvVC+zYwdg2xV2lFzjMIaFjdw6HZzMrl9KgzKAhnIePdLamqR06GcvsTyfxZ rTDVAaT/ohsDlDqR6tDsUcVOu8ISYMhJH2P6GSN/yy+/l3Ey4TwtfagAKpzf7ST8danw 6fdJxL06RIFx9ydK9Cq9l9Ogkf2tpcg/AMdH/6ovaipF7EOypchFWaOMCbVpGIo2hW4r /OTgN62oeUindQ4iiYVsDxGKKPE6p5FGNYvpRUNZ6VrvK9tLHPIVS98w4LpoGca/8RTn tWVWz1to5Esh3g3C9wjv7PY5OgAFRkGhBj4oGJP33CGecNSbCsy8ai9U+DwyG7EGX+Jx 8yqg== X-Gm-Message-State: ANoB5plChOnwB+zGOTv+SvHy100gTP/tTgN1z47eIb4iM+7u4+V1NsxO qduZ87FfdMiLw8zGujqS2mslvCw/1ARsPiix2eRt7w== X-Google-Smtp-Source: AA0mqf6W+h9P6ndCz0Dggo99+ASBIRvPTwqdxKgS71+gKGygKFJU/nFdcZ8e+IYnspiA5M16G/tzdKWR3tPtJqvust0= X-Received: by 2002:a05:6870:9d95:b0:13b:a163:ca6 with SMTP id pv21-20020a0568709d9500b0013ba1630ca6mr3240757oab.125.1668644366268; Wed, 16 Nov 2022 16:19:26 -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: <637576962dada_8cd03208b0@john.notmuch> From: Stanislav Fomichev Date: Wed, 16 Nov 2022 16:19:15 -0800 Message-ID: To: John Fastabend Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: LVOOGJGTNSQPEG5UXOTBSS4FXBPV5HZP X-Message-ID-Hash: LVOOGJGTNSQPEG5UXOTBSS4FXBPV5HZP 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: =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Martin KaFai Lau , bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, song@kernel.org, yhs@fb.com, kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org, David Ahern , Jakub Kicinski , Willem de Bruijn , Jesper Dangaard Brouer , Anatoly Burakov , Alexander Lobakin , Magnus Karlsson , Maryam Tahhan , xdp-hints@xdp-project.net, netdev@vger.kernel.org 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 3:47 PM John Fastabend w= rote: > > 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_METADATA= _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(XDP_M= ETADATA_KFUNC_RX_TIMESTAMP)) { > > > > >>>>>>> + /* return ktime_get_mono_fast_ns(); */ > > > > >>>>>>> + bpf_patch_append(patch, BPF_EMIT_CALL(ktime_g= et_mono_fast_ns)); > > > > >>>>>>> + } > > > > >>>>>>> +} > > > > >>>>>> > > > > >>>>>> So these look reasonable enough, but would be good to see so= me examples > > > > >>>>>> of kfunc implementations that don't just BPF_CALL to a kerne= l function > > > > >>>>>> (with those helper wrappers we were discussing before). > > > > >>>>> > > > > >>>>> Let's maybe add them if/when needed as we add more metadata s= upport? > > > > >>>>> xdp_metadata_export_to_skb has an example, and rfc 1/2 have m= ore > > > > >>>>> 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 to ma= intain the > > > > >>>> BPF code generation in the drivers is probably the biggest dra= wback of > > > > >>>> the kfunc approach, so it would be good to be relatively sure = that we > > > > >>>> can manage that complexity (via helpers) before we commit to t= his :) > > > > >>> > > > > >>> Right, and I've added a bunch of examples in v2 rfc so we can j= udge > > > > >>> whether that complexity is manageable or not :-) > > > > >>> Do you want me to add those wrappers you've back without any re= al users? > > > > >>> Because I had to remove my veth tstamp accessors due to John/Je= sper > > > > >>> 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 good to s= ee some > > > > >> examples of kfunc implementations that don't just BPF_CALL to a = kernel > > > > >> function"? In this case do you mean BPF code directly without th= e call? > > > > >> > > > > >> Early on I thought we should just expose the rx_descriptor which= would > > > > >> be roughly the same right? (difference being code embedded in dr= iver vs > > > > >> a lib) Trouble I ran into is driver code using seqlock_t and mut= exs > > > > >> which wasn't as straight forward as the simpler just read it fro= m > > > > >> 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_cqe *)cq= e; > > > > >> > > > > >> 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->clock, tim= estamp); > > > > >> } 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 have > > > > >> to create read_seqbegin, read_seqretry, mutex_lock, ... to get > > > > >> at least the mlx and ice drivers it looks like we would need som= e > > > > >> 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 BPF_CAL= L > > > > >> 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 + ((u6= 4)low)) > > > > > > > > > > static inline ktime_t mlx5_real_time_cyc2time(struct mlx5_clock *= clock, > > > > > u64 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 imp= act > > > > on the XDP data path (thinking mostly about the skb metadata case h= ere, > > > > 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 th= is > > > > series against Jesper's; which I think we should definitely be doin= g > > > > before merging this. > > > > > > Good point I got sort of singularly focused on timestamp because I ha= ve > > > 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 think > you also need to add CO-RE to be friendly for driver developers? Otherwis= e > they have to keep that read in sync with the descriptors? Also need to > 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?