Message-ID: <CALDO+SYK_4RfRBe7Z0n00wkPhKc1HwGmcGT34W0tVMVZFLqYpw@mail.gmail.com>
Date:   Mon, 26 Mar 2018 09:06:54 -0700
From:   William Tu <u9012063@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     magnus.karlsson@...el.com,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        willemdebruijn.kernel@...il.com,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com, jesse.brandeburg@...el.com,
        anjali.singhai@...el.com, jeffrey.b.shaw@...el.com,
        ferruh.yigit@...el.com, qi.z.zhang@...el.com
Subject: Re: [RFC PATCH 00/24] Introducing AF_XDP support

On Wed, Jan 31, 2018 at 5:53 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> This RFC introduces a new address family called AF_XDP that is
> optimized for high performance packet processing and zero-copy
> semantics. Throughput improvements can be up to 20x compared to V2 and
> V3 for the micro benchmarks included. Would be great to get your
> feedback on it. Note that this is the follow up RFC to AF_PACKET V4
> from November last year. The feedback from that RFC submission and the
> presentation at NetdevConf in Seoul was to create a new address family
> instead of building on top of AF_PACKET. AF_XDP is this new address
> family.
>
> The main difference between AF_XDP and AF_PACKET V2/V3 on a descriptor
> level is that TX and RX descriptors are separated from packet
> buffers. An RX or TX descriptor points to a data buffer in a packet
> buffer area. RX and TX can share the same packet buffer so that a
> packet does not have to be copied between RX and TX. Moreover, if a
> packet needs to be kept for a while due to a possible retransmit, then
> the descriptor that points to that packet buffer can be changed to
> point to another buffer and reused right away. This again avoids
> copying data.
>
> The RX and TX descriptor rings are registered with the setsockopts
> XDP_RX_RING and XDP_TX_RING, similar to AF_PACKET. The packet buffer
> area is allocated by user space and registered with the kernel using
> the new XDP_MEM_REG setsockopt. All these three areas are shared
> between user space and kernel space. The socket is then bound with a
> bind() call to a device and a specific queue id on that device, and it
> is not until bind is completed that traffic starts to flow.
>
> An XDP program can be loaded to direct part of the traffic on that
> device and queue id to user space through a new redirect action in an
> XDP program called bpf_xdpsk_redirect that redirects a packet up to
> the socket in user space. All the other XDP actions work just as
> before. Note that the current RFC requires the user to load an XDP
> program to get any traffic to user space (for example all traffic to
> user space with the one-liner program "return
> bpf_xdpsk_redirect();"). We plan on introducing a patch that removes
> this requirement and sends all traffic from a queue to user space if
> an AF_XDP socket is bound to it.
>
> AF_XDP can operate in three different modes: XDP_SKB, XDP_DRV, and
> XDP_DRV_ZC (shorthand for XDP_DRV with a zero-copy allocator as there
> is no specific mode called XDP_DRV_ZC). If the driver does not have
> support for XDP, or XDP_SKB is explicitly chosen when loading the XDP
> program, XDP_SKB mode is employed that uses SKBs together with the
> generic XDP support and copies out the data to user space. A fallback
> mode that works for any network device. On the other hand, if the
> driver has support for XDP (all three NDOs: ndo_bpf, ndo_xdp_xmit and
> ndo_xdp_flush), these NDOs, without any modifications, will be used by
> the AF_XDP code to provide better performance, but there is still a
> copy of the data into user space. The last mode, XDP_DRV_ZC, is XDP
> driver support with the zero-copy user space allocator that provides
> even better performance. In this mode, the networking HW (or SW driver
> if it is a virtual driver like veth) DMAs/puts packets straight into
> the packet buffer that is shared between user space and kernel
> space. The RX and TX descriptor queues of the networking HW are NOT
> shared to user space. Only the kernel can read and write these and it
> is the kernel driver's responsibility to translate these HW specific
> descriptors to the HW agnostic ones in the virtual descriptor rings
> that user space sees. This way, a malicious user space program cannot
> mess with the networking HW. This mode though requires some extensions
> to XDP.
>
> To get the XDP_DRV_ZC mode to work for RX, we chose to introduce a
> buffer pool concept so that the same XDP driver code can be used for
> buffers allocated using the page allocator (XDP_DRV), the user-space
> zero-copy allocator (XDP_DRV_ZC), or some internal driver specific
> allocator/cache/recycling mechanism. The ndo_bpf call has also been
> extended with two commands for registering and unregistering an XSK
> socket and is in the RX case mainly used to communicate some
> information about the user-space buffer pool to the driver.
>
> For the TX path, our plan was to use ndo_xdp_xmit and ndo_xdp_flush,
> but we run into problems with this (further discussion in the
> challenges section) and had to introduce a new NDO called
> ndo_xdp_xmit_xsk (xsk = XDP socket). It takes a pointer to a netdevice
> and an explicit queue id that packets should be sent out on. In
> contrast to ndo_xdp_xmit, it is asynchronous and pulls packets to be
> sent from the xdp socket (associated with the dev and queue
> combination that was provided with the NDO call) using a callback
> (get_tx_packet), and when they have been transmitted it uses another
> callback (tx_completion) to signal completion of packets. These
> callbacks are set via ndo_bpf in the new XDP_REGISTER_XSK
> command. ndo_xdp_xmit_xsk is exclusively used by the XDP socket code
> and thus does not clash with the XDP_REDIRECT use of
> ndo_xdp_xmit. This is one of the reasons that the XDP_DRV mode
> (without ZC) is currently not supported by TX. Please have a look at
> the challenges section for further discussions.
>
> The AF_XDP bind call acts on a queue pair (channel in ethtool speak),
> so the user needs to steer the traffic to the zero-copy enabled queue
> pair. Which queue to use, is up to the user.
>
> For an untrusted application, HW packet steering to a specific queue
> pair (the one associated with the application) is a requirement, as
> the application would otherwise be able to see other user space
> processes' packets. If the HW cannot support the required packet
> steering, XDP_DRV or XDP_SKB mode have to be used as they do not
> expose the NIC's packet buffer into user space as the packets are
> copied into user space from the NIC's packet buffer in the kernel.
>
> There is a xdpsock benchmarking/test application included. Say that
> you would like your UDP traffic from port 4242 to end up in queue 16,
> that we will enable AF_XDP on. Here, we use ethtool for this:
>
>       ethtool -N p3p2 rx-flow-hash udp4 fn
>       ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
>           action 16
>
> Running the l2fwd benchmark in XDP_DRV_ZC mode can then be done using:
>
>       samples/bpf/xdpsock -i p3p2 -q 16 -l -N
>
> For XDP_SKB mode, use the switch "-S" instead of "-N" and all options
> can be displayed with "-h", as usual.
>
> We have run some benchmarks on a dual socket system with two Broadwell
> E5 2660 @ 2.0 GHz with hyperthreading turned off. Each socket has 14
> cores which gives a total of 28, but only two cores are used in these
> experiments. One for TR/RX and one for the user space application. The
> memory is DDR4 @ 2133 MT/s (1067 MHz) and the size of each DIMM is
> 8192MB and with 8 of those DIMMs in the system we have 64 GB of total
> memory. The compiler used is gcc version 5.4.0 20160609. The NIC is an
> Intel I40E 40Gbit/s using the i40e driver.
>
> Below are the results in Mpps of the I40E NIC benchmark runs for 64
> byte packets, generated by commercial packet generator HW that is
> generating packets at full 40 Gbit/s line rate.
>
> XDP baseline numbers without this RFC:
> xdp_rxq_info --action XDP_DROP 31.3 Mpps
> xdp_rxq_info --action XDP_TX   16.7 Mpps
>
> XDP performance with this RFC i.e. with the buffer allocator:
> XDP_DROP 21.0 Mpps
> XDP_TX   11.9 Mpps
>
> AF_PACKET V4 performance from previous RFC on 4.14-rc7:
> Benchmark   V2     V3     V4     V4+ZC
> rxdrop      0.67   0.73   0.74   33.7
> txpush      0.98   0.98   0.91   19.6
> l2fwd       0.66   0.71   0.67   15.5
>
> AF_XDP performance:
> Benchmark   XDP_SKB   XDP_DRV    XDP_DRV_ZC (all in Mpps)
> rxdrop      3.3        11.6         16.9
> txpush      2.2         NA*         21.8
> l2fwd       1.7         NA*         10.4
>

Hi,
I also did an evaluation of AF_XDP, however the performance isn't as
good as above.
I'd like to share the result and see if there are some tuning suggestions.

System:
16 core, Intel(R) Xeon(R) CPU E5-2440 v2 @ 1.90GHz
Intel 10G X540-AT2 ---> so I can only run XDP_SKB mode

AF_XDP performance:
Benchmark   XDP_SKB
rxdrop      1.27 Mpps
txpush      0.99 Mpps
l2fwd        0.85 Mpps

NIC configuration:
the command
"ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 action 16"
doesn't work on my ixgbe driver, so I use ntuple:

ethtool -K enp10s0f0 ntuple on
ethtool -U enp10s0f0 flow-type udp4 src-ip 10.1.1.100 action 1
then
echo 1 > /proc/sys/net/core/bpf_jit_enable
./xdpsock -i enp10s0f0 -r -S --queue=1

I also take a look at perf result:
For rxdrop:
86.56%  xdpsock xdpsock           [.] main
  9.22%  xdpsock  [kernel.vmlinux]  [k] nmi
  4.23%  xdpsock  xdpsock         [.] xq_enq

For l2fwd:
20.81%  xdpsock xdpsock             [.] main
 10.64%  xdpsock [kernel.vmlinux]    [k] clflush_cache_range
  8.46%  xdpsock  [kernel.vmlinux]    [k] xsk_sendmsg
  6.72%  xdpsock  [kernel.vmlinux]    [k] skb_set_owner_w
  5.89%  xdpsock  [kernel.vmlinux]    [k] __domain_mapping
  5.74%  xdpsock  [kernel.vmlinux]    [k] alloc_skb_with_frags
  4.62%  xdpsock  [kernel.vmlinux]    [k] netif_skb_features
  3.96%  xdpsock  [kernel.vmlinux]    [k] ___slab_alloc
  3.18%  xdpsock  [kernel.vmlinux]    [k] nmi

I observed that the i40e's XDP_SKB result is much better than my ixgbe's result.
I wonder in XDP_SKB mode, does the driver make performance difference?
Or my cpu (E5-2440 v2 @ 1.90GHz) is too old?

Thanks
William

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