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[194.45.78.10]) by smtp.gmail.com with ESMTPSA id gx24-20020a170906f1d800b0092d16623eeasm16798089ejb.138.2023.03.29.11.19.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Mar 2023 11:20:00 -0700 (PDT) From: Jesper Dangaard Brouer X-Google-Original-From: Jesper Dangaard Brouer Message-ID: Date: Wed, 29 Mar 2023 20:19:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Cc: brouer@redhat.com, bpf@vger.kernel.org, netdev@vger.kernel.org, martin.lau@kernel.org, ast@kernel.org, daniel@iogearbox.net, alexandr.lobakin@intel.com, larysa.zaremba@intel.com, xdp-hints@xdp-project.net, anthony.l.nguyen@intel.com, yoong.siang.song@intel.com, boon.leong.ong@intel.com, intel-wired-lan@lists.osuosl.org, pabeni@redhat.com, jesse.brandeburg@intel.com, kuba@kernel.org, edumazet@google.com, john.fastabend@gmail.com, hawk@kernel.org, davem@davemloft.net Subject: Re: [PATCH bpf RFC 1/4] xdp: rss hash types representation Content-Language: en-US To: Stanislav Fomichev , Jesper Dangaard Brouer References: <168003451121.3027256.13000250073816770554.stgit@firesoul> <168003455815.3027256.7575362149566382055.stgit@firesoul> <811724e2-cdd6-15fe-b176-9dfcdbd98bad@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 29/03/2023 19.18, Stanislav Fomichev wrote: > On 03/29, Jesper Dangaard Brouer wrote: > >> On 28/03/2023 23.58, Stanislav Fomichev wrote: >> > On 03/28, Jesper Dangaard Brouer wrote: >> > > The RSS hash type specifies what portion of packet data NIC hardware used >> > > when calculating RSS hash value. The RSS types are focused on Internet >> > > traffic protocols at OSI layers L3 and L4. L2 (e.g. ARP) often get hash >> > > value zero and no RSS type. For L3 focused on IPv4 vs. IPv6, and L4 >> > > primarily TCP vs UDP, but some hardware supports SCTP. >> > >> > > Hardware RSS types are differently encoded for each hardware NIC. Most >> > > hardware represent RSS hash type as a number. Determining L3 vs L4 often >> > > requires a mapping table as there often isn't a pattern or sorting >> > > according to ISO layer. >> > >> > > The patch introduce a XDP RSS hash type (xdp_rss_hash_type) that can both >> > > be seen as a number that is ordered according by ISO layer, and can be bit >> > > masked to separate IPv4 and IPv6 types for L4 protocols. Room is available >> > > for extending later while keeping these properties. This maps and unifies >> > > difference to hardware specific hashes. >> > >> > Looks good overall. Any reason we're making this specific layout? > >> One important goal is to have a simple/fast way to determining L3 vs L4, >> because a L4 hash can be used for flow handling (e.g. load-balancing). > >> We below layout you can: > >>   if (rss_type & XDP_RSS_TYPE_L4_MASK) >>     bool hw_hash_do_LB = true; > >> Or using it as a number: > >>   if (rss_type > XDP_RSS_TYPE_L4) >>     bool hw_hash_do_LB = true; > > Why is it strictly better then the following? > > if (rss_type & (TYPE_UDP | TYPE_TCP | TYPE_SCTP)) {} > See V2 I dropped the idea of this being a number (that idea was not a good idea). > If we add some new L4 format, the bpf programs can be updated to support > it? > >> I'm very open to changes to my "specific" layout.  I am in doubt if >> using it as a number is the right approach and worth the trouble. > >> > Why not simply the following? >> > >> > enum { >> >  ����XDP_RSS_TYPE_NONE = 0, >> >  ����XDP_RSS_TYPE_IPV4 = BIT(0), >> >  ����XDP_RSS_TYPE_IPV6 = BIT(1), >> >  ����/* IPv6 with extension header. */ >> >  ����/* let's note ^^^ it in the UAPI? */ >> >  ����XDP_RSS_TYPE_IPV6_EX = BIT(2), >> >  ����XDP_RSS_TYPE_UDP = BIT(3), >> >  ����XDP_RSS_TYPE_TCP = BIT(4), >> >  ����XDP_RSS_TYPE_SCTP = BIT(5), > >> We know these bits for UDP, TCP, SCTP (and IPSEC) are exclusive, they >> cannot be set at the same time, e.g. as a packet cannot both be UDP and >> TCP.  Thus, using these bits as a number make sense to me, and is more >> compact. > > [..] > >> This BIT() approach also have the issue of extending it later (forward >> compatibility).  As mentioned a common task will be to check if >> hash-type is a L4 type.  See mlx5 [patch 4/4] needed to extend with >> IPSEC. Notice how my XDP_RSS_TYPE_L4_MASK covers all the bits that this >> can be extended with new L4 types, such that existing progs will still >> work checking for L4 check.  It can of-cause be solved in the same way >> for this BIT() approach by reserving some bits upfront in a mask. > > We're using 6 bits out of 64, we should be good for awhile? If there > is ever a forward compatibility issue, we can always come up with > a new kfunc. I want/need store the RSS-type in the xdp_frame, for XDP_REDIRECT and SKB use-cases. Thus, I don't want to use 64-bit/8-bytes, as xdp_frame size is limited (given it reduces headroom expansion). > > One other related question I have is: should we export the type > over some additional new kfunc argument? (instead of abusing the return > type) Good question. I was also wondering if it wouldn't be better to add another kfunc argument with the rss_hash_type? That will change the call signature, so that will not be easy to handle between kernel releases. > Maybe that will let us drop the explicit BTF_TYPE_EMIT as well? Sure, if we define it as an argument, then it will automatically exported as BTF. >> > } >> > >> > And then using XDP_RSS_TYPE_IPV4|XDP_RSS_TYPE_UDP vs >> > XDP_RSS_TYPE_IPV6|XXX ? > >> Do notice, that I already does some level of or'ing ("|") in this >> proposal.  The main difference is that I hide this from the driver, and >> kind of pre-combine the valid combination (enum's) drivers can select >> from. I do get the point, and I think I will come up with a combined >> solution based on your input. > > >> The RSS hashing types and combinations comes from M$ standards: >>   [1] >> https://learn.microsoft.com/en-us/windows-hardware/drivers/network/rss-hashing-types#ipv4-hash-type-combinations > > My main concern here is that we're over-complicating it with the masks > and the format. With the explicit bits we can easily map to that > spec you mention. See if you like my RFC-V2 proposal better. It should go more in your direction. > > For example, for forward compat, I'm not sure we can assume that the people > will do: >     "rss_type & XDP_RSS_TYPE_L4_MASK" > instead of something like: >     "rss_type & (XDP_RSS_TYPE_L4_IPV4_TCP|XDP_RSS_TYPE_L4_IPV4_UDP)" > This code is allowed in V2 and should be. It is a choice of BPF-programmer in line-2 to not be forward compatible with newer L4 types. >> > > This proposal change the kfunc API bpf_xdp_metadata_rx_hash() to return >> > > this RSS hash type on success. This is the real question (as also raised above)... Should we use return value or add an argument for type? --Jesper