From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 48A1D39C for ; Fri, 18 Aug 2023 02:09:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54782C433C7; Fri, 18 Aug 2023 02:09:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692324598; bh=3fB+vAoFtqXbB6GVaM4eS1td9RpyllU4lr6gezSpNIA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=cikJWNOI36FGPE2ohzmBfqWtYQgDe5bj93Rqcn5YnQ17xoKLYj3rlGmvY/jReQ8zG JRnwC5W5XDGDui5GkGsukBotbiV2Dg5ab8hwLilLNmDnnPHmkHGGt51b3JjMarzVTO jPxbnzKXLe/bBDAIzNtQPP6rvzYH30Gr3HLAmSlwfnFZELp2rz+GbyZbGgNbhl33O6 8rGhKiXnpk6K7OQHDI+oHS9sqv+fNq9zv1flYOu28qWHwYHLqlzn1L4ktmE9JqlqJc K/xmJRp7qO9iHfcGTXZhj8+qvvsNaivUL7y57W2S9HcIpP2zicjHq9+8zWsI56vImf U96wT8dMd1zEA== Date: Thu, 17 Aug 2023 19:09:57 -0700 From: Jakub Kicinski To: David Ahern Cc: Willem de Bruijn , Mina Almasry , netdev@vger.kernel.org, Eric Dumazet , Paolo Abeni , Jesper Dangaard Brouer , Ilias Apalodimas , Magnus Karlsson , sdf@google.com, Willem de Bruijn , Kaiyuan Zhang Subject: Re: [RFC PATCH v2 02/11] netdev: implement netlink api to bind dma-buf to netdevice Message-ID: <20230817190957.571ab350@kernel.org> In-Reply-To: References: <20230810015751.3297321-1-almasrymina@google.com> <20230810015751.3297321-3-almasrymina@google.com> <7dd4f5b0-0edf-391b-c8b4-3fa82046ab7c@kernel.org> <20230815171638.4c057dcd@kernel.org> <64dcf5834c4c8_23f1f8294fa@willemb.c.googlers.com.notmuch> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 17 Aug 2023 19:33:47 -0600 David Ahern wrote: > [ sorry for the delayed response; very busy 2 days ] Tell me about it :) > On 8/16/23 10:12 AM, Willem de Bruijn wrote: > > Jakub Kicinski wrote: > >> Let's start sketching out the design for queue config. > >> Without sliding into scope creep, hopefully. > >> > >> Step one - I think we can decompose the problem into: > >> A) flow steering > >> B) object lifetime and permissions > >> C) queue configuration (incl. potentially creating / destroying queues) > >> > >> These come together into use scenarios like: > >> #1 - partitioning for containers - when high perf containers share > >> a machine each should get an RSS context on the physical NIC > >> to have predictable traffic<>CPU placement, they may also have > >> different preferences on how the queues are configured, maybe > >> XDP, too? > > subfunctions are a more effective and simpler solution for containers, no? Maybe, subfunctions offload a lot, let's not go too far into the weeds on production and flexibility considerations but they wouldn't be my first choice. > >> #2 - fancy page pools within the host (e.g. huge pages) > >> #3 - very fancy page pools not within the host (Mina's work) > >> #4 - XDP redirect target (allowing XDP_REDIRECT without installing XDP > >> on the target) > >> #5 - busy polling - admittedly a bit theoretical, I don't know of > >> anyone busy polling in real life, but one of the problems today > >> is that setting it up requires scraping random bits of info from > >> sysfs and a lot of hoping. > >> > >> Flow steering (A) is there today, to a sufficient extent, I think, > >> so we can defer on that. Sooner or later we should probably figure > >> out if we want to continue down the unruly path of TC offloads or > >> just give up and beef up ethtool. > > Flow steering to TC offloads -- more details on what you were thinking here? I think TC flower can do almost everything ethtool -N can. So do we continue to developer for both APIs or pick one? > >> I don't have a good sense of what a good model for cleanup and > >> permissions is (B). All I know is that if we need to tie things to > >> processes netlink can do it, and we shouldn't have to create our > >> own FS and special file descriptors... > > From my perspective the main sticking point that has not been handled is > flushing buffers from the RxQ, but there is 100% tied to queue > management and a process' ability to effect a flush or queue tear down - > and that is the focus of your list below: If you're thinking about it from the perspective of "application died give me back all the buffers" - the RxQ is just one piece, right? As we discovered with page pool - packets may get stuck in stack for ever. > >> And then there's (C) which is the main part to talk about. > >> The first step IMHO is to straighten out the configuration process. > >> Currently we do: > >> > >> user -> thin ethtool API --------------------> driver > >> netdev core <---' > >> > >> By "straighten" I mean more of a: > >> > >> user -> thin ethtool API ---> netdev core ---> driver > >> > >> flow. This means core maintains the full expected configuration, > >> queue count and their parameters and driver creates those queues > >> as instructed. > >> > >> I'd imagine we'd need 4 basic ops: > >> - queue_mem_alloc(dev, cfg) -> queue_mem > >> - queue_mem_free(dev, cfg, queue_mem) > >> - queue_start(dev, queue info, cfg, queue_mem) -> errno > >> - queue_stop(dev, queue info, cfg) > >> > >> The mem_alloc/mem_free takes care of the commonly missed requirement to > >> not take the datapath down until resources are allocated for new config. > > sounds reasonable. > > >> > >> Core then sets all the queues up after ndo_open, and tears down before > >> ndo_stop. In case of an ethtool -L / -G call or enabling / disabling XDP > >> core can handle the entire reconfiguration dance. > > `ethtool -L/-G` and `ip link set {up/down}` pertain to the "general OS" > queues managed by a driver for generic workloads and networking > management (e.g., neigh discovery, icmp, etc). The discussions here > pertains to processes wanting to use their own memory or GPU memory in a > queue. Processes will come and go and the queue management needs to > align with that need without affecting all of the other queues managed > by the driver. For sure, I'm just saying that both the old uAPI can be translated to the new driver API, and so should the new uAPIs. I focused on the driver facing APIs because I think that it's the hard part. We have many drivers, the uAPI is more easily dreamed up, no? > >> The cfg object needs to contain all queue configuration, including > >> the page pool parameters. > >> > >> If we have an abstract model of the configuration in the core we can > >> modify it much more easily, I hope. I mean - the configuration will be > >> somewhat detached from what's instantiated in the drivers. > >> > >> I'd prefer to go as far as we can without introducing a driver callback > >> to "check if it can support a config change", and try to rely on > >> (static) capabilities instead. This allows more of the validation to > >> happen in the core and also lends itself naturally to exporting the > >> capabilities to the user. > >> > >> Checking the use cases: > >> > >> #1 - partitioning for containers - storing the cfg in the core gives > >> us a neat ability to allow users to set the configuration on RSS > >> context > >> #2, #3 - page pools - we can make page_pool_create take cfg and read whatever > >> params we want from there, memory provider, descriptor count, recycling > >> ring size etc. Also for header-data-split we may want different settings > >> per queue so again cfg comes in handy > >> #4 - XDP redirect target - we should spawn XDP TX queues independently from > >> the XDP configuration > >> > >> That's all I have thought up in terms of direction. > >> Does that make sense? What are the main gaps? Other proposals? > > > > More on (A) and (B): > > > > I expect most use cases match the containerization that you mention. > > Where a privileged process handles configuration. > > > > For that, the existing interfaces of ethtool -G/-L-/N/-K/-X suffice. > > > > A more far-out approach could infer the ntuple 5-tuple connection or > > 3-tuple listener rule from a socket itself, no ethtool required. But > > let's ignore that for now. > > > > Currently we need to use ethtool -X to restrict the RSS indirection > > table to a subset of queues. It is not strictly necessary to > > reconfigure the device on each new container, if pre-allocation a > > sufficient set of non-RSS queues. > > This is an interesting approach: This scheme here is along the lines of > you have N cpus in the server, so N queue sets (or channels). The > indirection table means M queue sets are used for RSS leaving N-M queues > for flows with "fancy memory providers". Such a model can work but it is > quite passive, needs careful orchestration and has a lot of moving, > disjointed pieces - with some race conditions around setup vs first data > packet arriving. > > I was thinking about a more generic design where H/W queues are created > and destroyed - e.g., queues unique to a process which makes the cleanup > so much easier. FWIW what Willem describes is what we were telling people to do for AF_XDP for however many years it existed. > > Then only ethtool -N is needed to drive data towards one of the > > non-RSS queues. Or one of the non context 0 RSS contexts if that is > > used. > > > > The main part that is missing is memory allocation. Memory is stranded > > on unused queues, and there is no explicit support for special > > allocators. > > > > A poor man's solution might be to load a ring with minimal sized > > buffers (assuming devices accept that, say a zero length buffer), > > attach a memory provider before inserting an ntuple rule, and refill > > from the memory provider. This requires accepting that a whole ring of > > packets is lost before refilled slots get filled.. > > > > (I'm messing with that with AF_XDP right now: a process that xsk_binds > > before filling the FILL queue..) > > > > Ideally, we would have a way to reconfigure a single queue, without > > having to down/up the entire device.. > > > > I don't know if the kernel needs an explicit abstract model, or can > > leave that to the userspace privileged daemon that presses the ethtool > > buttons. > > The kernel has that in the IB verbs S/W APIs. Yes, I realize that > comment amounts to profanity on this mailing list, but it should not be. > There are existing APIs for creating, managing and destroying queues - > open source, GPL'ed, *software* APIs that are open for all to use. > > That said, I have no religion here. If the netdev stack wants new APIs > to manage queues - including supplying buffers - drivers will have APIs > that can be adapted to some new ndo to create, configure, and destroy > queues. The ethtool API can be updated to manage that. Ultimately I > believe anything short of dynamic queue management will be a band-aid > approach that will have a lot of problems. No religion here either, but the APIs we talk about are not particularly complex. Having started hacking things together with page pools, huge pages, RSS etc - IMHO the reuse and convergence would be very superficial.