From: Jakub Kicinski <kuba@kernel•org>
To: David Ahern <dsahern@kernel•org>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail•com>,
Mina Almasry <almasrymina@google•com>,
netdev@vger•kernel.org, Eric Dumazet <edumazet@google•com>,
Paolo Abeni <pabeni@redhat•com>,
Jesper Dangaard Brouer <hawk@kernel•org>,
Ilias Apalodimas <ilias.apalodimas@linaro•org>,
Magnus Karlsson <magnus.karlsson@intel•com>,
sdf@google•com, Willem de Bruijn <willemb@google•com>,
Kaiyuan Zhang <kaiyuanz@google•com>
Subject: Re: [RFC PATCH v2 02/11] netdev: implement netlink api to bind dma-buf to netdevice
Date: Thu, 17 Aug 2023 19:09:57 -0700 [thread overview]
Message-ID: <20230817190957.571ab350@kernel.org> (raw)
In-Reply-To: <c47219db-abf9-8a5c-9b26-61f65ae4dd26@kernel.org>
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.
next prev parent reply other threads:[~2023-08-18 2:09 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-10 1:57 [RFC PATCH v2 00/11] Device Memory TCP Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 01/11] net: add netdev netlink api to bind dma-buf to a net device Mina Almasry
2023-08-10 16:04 ` Samudrala, Sridhar
2023-08-11 2:19 ` Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 02/11] netdev: implement netlink api to bind dma-buf to netdevice Mina Almasry
2023-08-13 11:26 ` Leon Romanovsky
2023-08-14 1:10 ` David Ahern
2023-08-14 3:15 ` Mina Almasry
2023-08-16 0:16 ` Jakub Kicinski
2023-08-16 16:12 ` Willem de Bruijn
2023-08-18 1:33 ` David Ahern
2023-08-18 2:09 ` Jakub Kicinski [this message]
2023-08-18 2:21 ` David Ahern
2023-08-18 21:52 ` Mina Almasry
2023-08-19 1:34 ` David Ahern
2023-08-19 2:06 ` Jakub Kicinski
2023-08-19 3:30 ` David Ahern
2023-08-19 14:18 ` Willem de Bruijn
2023-08-19 17:59 ` Mina Almasry
2023-08-21 21:16 ` Jakub Kicinski
2023-08-22 0:38 ` Willem de Bruijn
2023-08-22 1:51 ` Jakub Kicinski
2023-08-22 3:19 ` David Ahern
2023-08-30 12:38 ` Yunsheng Lin
2023-09-08 0:47 ` David Wei
2023-08-10 1:57 ` [RFC PATCH v2 03/11] netdev: implement netdevice devmem allocator Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 04/11] memory-provider: updates to core provider API for devmem TCP Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 05/11] memory-provider: implement dmabuf devmem memory provider Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 06/11] page-pool: add device memory support Mina Almasry
2023-08-19 9:51 ` Jesper Dangaard Brouer
2023-08-19 14:08 ` Willem de Bruijn
2023-08-19 15:22 ` Jesper Dangaard Brouer
2023-08-19 15:49 ` David Ahern
2023-08-19 16:12 ` Willem de Bruijn
2023-08-21 21:31 ` Jakub Kicinski
2023-08-22 0:58 ` Willem de Bruijn
2023-08-19 16:11 ` Willem de Bruijn
2023-08-19 20:24 ` Mina Almasry
2023-08-19 20:27 ` Mina Almasry
2023-09-08 2:32 ` David Wei
2023-08-22 6:05 ` Mina Almasry
2023-08-22 12:24 ` Jesper Dangaard Brouer
2023-08-22 23:33 ` Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 07/11] net: support non paged skb frags Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 08/11] net: add support for skbs with unreadable frags Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 09/11] tcp: implement recvmsg() RX path for devmem TCP Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 10/11] net: add SO_DEVMEM_DONTNEED setsockopt to release RX pages Mina Almasry
2023-08-10 1:57 ` [RFC PATCH v2 11/11] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
2023-08-10 10:29 ` [RFC PATCH v2 00/11] Device Memory TCP Christian König
2023-08-10 16:06 ` Jason Gunthorpe
2023-08-10 18:44 ` Mina Almasry
2023-08-10 18:58 ` Jason Gunthorpe
2023-08-11 1:56 ` Mina Almasry
2023-08-11 11:02 ` Christian König
2023-08-14 1:12 ` David Ahern
2023-08-14 2:11 ` Mina Almasry
2023-08-17 18:00 ` Pavel Begunkov
2023-08-17 22:18 ` Mina Almasry
2023-08-23 22:52 ` David Wei
2023-08-24 3:35 ` David Ahern
2023-08-15 13:38 ` David Laight
2023-08-15 14:41 ` Willem de Bruijn
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