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Tue, 06 Apr 2021 15:19:59 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id lt22sm7969970ejb.115.2021.04.06.15.19.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Apr 2021 15:19:58 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 54A5018030A; Wed, 7 Apr 2021 00:19:57 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: John Fastabend , Hangbin Liu Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Jiri Benc , Jesper Dangaard Brouer , Eelco Chaudron , ast@kernel.org, Daniel Borkmann , Lorenzo Bianconi , David Ahern , Andrii Nakryiko , Alexei Starovoitov , Maciej Fijalkowski , =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= Subject: Re: [PATCHv4 bpf-next 2/4] xdp: extend xdp_redirect_map with broadcast support In-Reply-To: <606cd787d64da_22ba520855@john-XPS-13-9370.notmuch> References: <20210402121954.3568992-1-liuhangbin@gmail.com> <20210402121954.3568992-3-liuhangbin@gmail.com> <606baa5025735_d46462085b@john-XPS-13-9370.notmuch> <20210406063819.GF2900@Leo-laptop-t470s> <878s5v4swp.fsf@toke.dk> <606cd787d64da_22ba520855@john-XPS-13-9370.notmuch> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 07 Apr 2021 00:19:57 +0200 Message-ID: <87k0pf2gz6.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org John Fastabend writes: > Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> Hangbin Liu writes: >>=20 >> > On Mon, Apr 05, 2021 at 05:24:48PM -0700, John Fastabend wrote: >> >> Hangbin Liu wrote: >> >> > This patch add two flags BPF_F_BROADCAST and BPF_F_EXCLUDE_INGRESS = to extend >> >> > xdp_redirect_map for broadcast support. >> >> >=20 >> >> > Keep the general data path in net/core/filter.c and the native data >> >> > path in kernel/bpf/devmap.c so we can use direct calls to get better >> >> > performace. >> >> >=20 >> >> > Here is the performance result by using xdp_redirect_{map, map_mult= i} in >> >> > sample/bpf and send pkts via pktgen cmd: >> >> > ./pktgen_sample03_burst_single_flow.sh -i eno1 -d $dst_ip -m $dst_m= ac -t 10 -s 64 >> >> >=20 >> >> > There are some drop back as we need to loop the map and get each in= terface. >> >> >=20 >> >> > Version | Test | Generic | = Native >> >> > 5.12 rc2 | redirect_map i40e->i40e | 2.0M | = 9.8M >> >> > 5.12 rc2 | redirect_map i40e->veth | 1.8M | = 12.0M >> >>=20 >> >> Are these are 10gbps i40e ports? Sorry if I asked this earlier, maybe >> >> add a note in the commit if another respin is needed. >> > >> > Yes, I will add it if there is an update. >> > >> >> > diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c >> >> > index 3980fb3bfb09..c8452c5f40f8 100644 >> >> > --- a/kernel/bpf/devmap.c >> >> > +++ b/kernel/bpf/devmap.c >> >> > @@ -198,6 +198,7 @@ static void dev_map_free(struct bpf_map *map) >> >> > list_del_rcu(&dtab->list); >> >> > spin_unlock(&dev_map_lock); >> >> >=20=20 >> >> > + bpf_clear_redirect_map(map); >> >>=20 >> >> Is this a bugfix? If its needed here wouldn't we also need it in the >> >> devmap case. >> > >> > No, in ee75aef23afe ("bpf, xdp: Restructure redirect actions") this fu= nction >> > was removed. I added it back as we use ri->map again. >> > >> > What devmap case you mean? >> > >> >>=20 >> >> > synchronize_rcu(); >> >> >=20=20 >> >> > /* Make sure prior __dev_map_entry_free() have completed. */ >> >>=20 >> >> [...] >> >>=20 >> >> > + >> >> > +static struct bpf_dtab_netdev *devmap_get_next_obj(struct xdp_buff= *xdp, >> >> > + struct bpf_map *map, >> >> > + u32 *key, u32 *next_key, >> >> > + int ex_ifindex) >> >> > +{ >> >> > + struct bpf_dtab_netdev *obj; >> >> > + struct net_device *dev; >> >> > + u32 index; >> >> > + int err; >> >> > + >> >> > + err =3D devmap_get_next_key(map, key, next_key); >> >> > + if (err) >> >> > + return NULL; >> >> > + >> >> > + /* When using dev map hash, we could restart the hashtab traversal >> >> > + * in case the key has been updated/removed in the mean time. >> >> > + * So we may end up potentially looping due to traversal restarts >> >> > + * from first elem. >> >> > + * >> >> > + * Let's use map's max_entries to limit the loop number. >> >> > + */ >> >> > + for (index =3D 0; index < map->max_entries; index++) { >> >> > + obj =3D devmap_lookup_elem(map, *next_key); >> >> > + if (!obj || dst_dev_is_ingress(obj, ex_ifindex)) >> >> > + goto find_next; >> >> > + >> >> > + dev =3D obj->dev; >> >> > + >> >> > + if (!dev->netdev_ops->ndo_xdp_xmit) >> >> > + goto find_next; >> >> > + >> >> > + err =3D xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data); >> >> > + if (unlikely(err)) >> >> > + goto find_next; >> >> > + >> >> > + return obj; >> >> > + >> >> > +find_next: >> >> > + key =3D next_key; >> >> > + err =3D devmap_get_next_key(map, key, next_key); >> >> > + if (err) >> >> > + break; >> >> > + } >> >>=20 >> >> I'm missing something. Either an elaborated commit message or comment >> >> is probably needed. I've been looking at this block for 30 minutes and >> >> can't see how we avoid sending duplicate frames on a single interface? >> >> Can you check this code flow,=20 >> >>=20 >> >> dev_map_enqueue_multi() >> >> for (;;) { >> >> next_obj =3D devmap_get_next_obj(...) >> >> for (index =3D 0; index < map->max_entries; index++) { >> >> obj =3D devmap_lookup_elem(); >> >> if (!obj) goto find_next >> >> key =3D next_key; >> >> err =3D devmap_get_next_key()=20 >> >> if (!key) goto find_first >> >> for (i =3D 0; i < dtab->n_buckets; i++) >> >> return *next <- now *next_key is point back >> >> at first entry >> >> // loop back through and find first obj and return that >> > >> > devmap_get_next_key() will loop to find the first one if there is no >> > key or dev. In normal time it will stop after the latest one. >> >> } >> >> bq_enqueue(...) // enqueue original obj >> >> obj =3D next_obj; >> >> key =3D next_key;=20 >> >> ... // we are going to enqueue first obj, but how do we know >> >> // this hasn't already been sent? Presumably if we have >> >> // a delete in the hash table in the middle of a multicast >> >> // operation this might happen? >> >> } >> > >> > And yes, there is an corner case that if we removed a dev during multi= cast, >> > there is an possibility that restart from the first key. But given that >> > this is an unlikely case, and in normal internet there is also a possi= bility >> > of duplicate/lost packet. This should also be acceptable? >>=20 >> In my mind this falls under "acceptable corner cases". I.e., if you're >> going to use the map for redirect and you expect to be updating it while >> you're doing so, don't use a hashmap. But if you will not be updating >> the map (or find the possible duplication acceptable), you can use the >> hashmap and gain the benefit of being able to index by ifindex. > > In a Kubernetes setup its going to be hard, if possible at all, to restri= ct > the map from moving as interfaces/IPs are going to be dynamic. Using a > hash map has nice benefits of not having to figure out how to put ifindex= 's > into the array. Although on some early implementations I wrote a small > hashing algorithm over the top of array, so that could work. > > I don't know how well multicast applications might handle duplicate packe= ts. > I wouldn't be too surprised if it was problematic. On the other hand miss= ing > an entry that was just added is likely OK. There is no way to know from > network/user side if the entry was actually added before multicast op and > skipped or insert happened just after multicast op. And vice versa for a > delete dev, no way to know the multicast op happened before/after the > delete. > > Have we consider doing something like the batch lookup ops over hashtab? > I don't mind "missing" values so if we just walk the list? > > head =3D dev_map_index_hash(dtab, i) > // collect all my devs and get ready to send multicast > hlist_nulls_for_each_entry_safe(dev, next, head, index_hlist) { > enqueue(dev, skb) > } > // submit the queue of entries and do all the work to actually xmit > submit_enqueued(); > > We don't have to care about keys just walk the hash list? So you'd wrap that in a loop like: for (i =3D 0; i < dtab->n_buckets; i++) { head =3D dev_map_index_hash(dtab, i); hlist_nulls_for_each_entry_safe(dev, next, head, index_hlist) { bq_enqueue(dev, xdpf, dev_rx, obj->xdp_prog); } } or? Yeah, I guess that would work! It would mean that dev_map_enqueue_multi() would need more in-depth knowledge into the map type, so would likely need to be two different functions for the two different map types, living in devmap.c - but that's probably acceptable. And while we're doing that, the array-map version can also loop over all indexes up to max_entries, instead of stopping at the first index that doesn't have an entry like it does now (right now, it looks like if you populate entries 0 and 2 in an array-map only one copy of the packet will be sent, to index 0). It makes it a bit more awkward to do Hangbin's clever trick to avoid doing an extra copy by aborting the loop early. But I guess the same technique could apply... -Toke