From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by mail.toke.dk (Postfix) with ESMTPS id C52939C2E46 for ; Thu, 17 Nov 2022 03:17:54 +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=c/Tv2c61 Received: by mail-ej1-x62c.google.com with SMTP id gv23so1720189ejb.3 for ; Wed, 16 Nov 2022 18:17:54 -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=YeytEidfg15z3/Kw1ktwj9CpONuWGAQGvGODy3kxHnY=; b=c/Tv2c61i2D66P7Kb2wyOGck/L6qhzrUL0My7v4/oFLEi+htJTSRd/SHiGwaEf7uty gSNu3v0ptlwDxAhU/iI7sL4Or7EXZXAj6OCFe2/oaGapnmAelkSWoIDnrbxgj8gBELuK uAoWqA8DOutThFxlH7BcfAjP36ZOolKYTSzD+2j/fLAfQwA3dX/3/9qDY0iQ5XP0HkiP wzWZZRNTpxiaMHByrRQzR1IYvXYTZsdRK4/2aEcWwMztum1OGLwOoimsQbemXAfioyPR s5Bmv9vytJiWtvlkHwXbv4wizo5bjr44nsOIblv6TPuZzvWwjC3sGxsDB3bNSB51DB2L iuvg== 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=YeytEidfg15z3/Kw1ktwj9CpONuWGAQGvGODy3kxHnY=; b=i5UIozw1I+OhmBZVQylhhx3Lnx5O+os6k6tTEfcEtPohuC9f5SgAfiJpSPCEhNSkeQ +C8IEUooUOMBezX6Jh6GZP9F0wcNGcFFGBFuCbPcQ0IeIyGE+Snp2KQQCslj+q6a3uz1 R0G5VKFZaeAGT61gKyfHQxw51thD1Z+4xB9tMnLdvRh39Y0Cjs7sbU5ts7fRjhXUQ+Jh dli9f/iTm6T+mkbktPuGOGYjtQ1NOBniEoBtHjSQ12mUqMgw19chbplQa4baQZXeMaCo ptmVgbtM43vYvV/mJCTYmA+BTW0QfstjqhuoPPp0RC9G9c2uOWeOo3pyJGfhP5mK7sXI UTLA== X-Gm-Message-State: ANoB5plI++vtRR1lKcIlJwLTzaZ7mMvCpfxFTVCsE55GRlkuWbv4hO7Q Gq4kUNOxMXU8jwr2cHIAQMLqSJcY7ENKyGantZ4= X-Google-Smtp-Source: AA0mqf4+ANk95VTDlgtbyy0jqe3omnZdq2vpU3YAZkeLykrRKdTF8i/UPdIoYxa2UhcbnfldSIhUpAAezbRvpdl+edQ= X-Received: by 2002:a17:906:4351:b0:78d:513d:f447 with SMTP id z17-20020a170906435100b0078d513df447mr444304ejm.708.1668651472434; Wed, 16 Nov 2022 18:17:52 -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 18:17:40 -0800 Message-ID: To: Stanislav Fomichev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: 6A77HKGLV7WA7H3MMENLIFXBE3GS7HR5 X-Message-ID-Hash: 6A77HKGLV7WA7H3MMENLIFXBE3GS7HR5 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 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 *pro= g, u32 func_id, > > > > > >>>>>>> + struct bpf_patch *patch) > > > > > >>>>>>> +{ > > > > > >>>>>>> + if (func_id =3D=3D xdp_metadata_kfunc_id(XDP_METADA= TA_KFUNC_RX_TIMESTAMP_SUPPORTED)) { > > > > > >>>>>>> + /* return true; */ > > > > > >>>>>>> + bpf_patch_append(patch, BPF_MOV64_IMM(BPF_R= EG_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(ktime= _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 ker= nel function > > > > > >>>>>> (with those helper wrappers we were discussing before). > > > > > >>>>> > > > > > >>>>> Let's maybe add them if/when needed as we add more metadata= 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 them ba= ck 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 biggest d= rawback of > > > > > >>>> the kfunc approach, so it would be good to be relatively sur= e 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 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 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 "would be good 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 without = the call? > > > > > >> > > > > > >> Early on I thought we should just expose the rx_descriptor whi= ch 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 and m= utexs > > > > > >> which wasn't as straight forward as the simpler just read it f= rom > > > > > >> the descriptor. For example in mlx getting the ts would be eas= y 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) + !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, t= imestamp); > > > > > >> } 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 hav= e > > > > > >> to create read_seqbegin, read_seqretry, mutex_lock, ... to get > > > > > >> at least the mlx and ice drivers it looks like we would need s= ome > > > > > >> more BPF primitives/helpers. Looks like some more work is need= ed > > > > > >> on ice driver though to get rx tstamps on all packets. > > > > > >> > > > > > >> Anyways this convinced me real devices will probably use BPF_C= ALL > > > > > >> 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_clock= *clock, > > > > > > u64 timestamp) > > > > > > { > > > > > > u64 time =3D REAL_TIME_TO_NS(timestamp >> 32, timestam= p & 0xFFFFFFFF); > > > > > > > > > > > > return ns_to_ktime(time); > > > > > > } > > > > > > > > > > > > If some hints are harder to get, then just doing a kfunc call i= s better. > > > > > > > > > > Sure, but if we end up having a full function call for every fiel= d in > > > > > the metadata, that will end up having a significant performance i= mpact > > > > > 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 definitely be do= ing > > > > > 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 th= e > > > rx side for a v2. > > > > If you go with in-kernel BPF kfunc approach (vs user space side) I thin= k > > you also need to add CO-RE to be friendly for driver developers? Otherw= ise > > 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? 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).