Message-ID: <CAKgT0Ufya10bXa4BXFbR2GtwZM6i7x8LPYoodFPZ82=S+t7x2w@mail.gmail.com>
Date:   Mon, 26 Mar 2018 16:03:20 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Tushar Dave <tushar.n.dave@...cle.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        William Tu <u9012063@...il.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Willem de Bruijn <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,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        Anjali Singhai Jain <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 Mon, Mar 26, 2018 at 3:54 PM, Tushar Dave <tushar.n.dave@...cle.com> wrote:
>
>
> On 03/26/2018 09:38 AM, Jesper Dangaard Brouer wrote:
>>
>>
>> On Mon, 26 Mar 2018 09:06:54 -0700 William Tu <u9012063@...il.com> wrote:
>>
>>> 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
>>
>>
>> Hmmm, why is X540-AT2 not able to use XDP natively?
>>
>>> AF_XDP performance:
>>> Benchmark   XDP_SKB
>>> rxdrop      1.27 Mpps
>>> txpush      0.99 Mpps
>>> l2fwd        0.85 Mpps
>>
>>
>> Definitely too low...
>>
>> What is the performance if you drop packets via iptables?
>>
>> Command:
>>   $ iptables -t raw -I PREROUTING -p udp --dport 9 --j DROP
>>
>>> 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
>>
>>
>> It looks very strange that you see non-maskable interrupt's (NMI) being
>> this high...
>>
>>
>>>
>>> For l2fwd:
>>>   20.81%  xdpsock xdpsock             [.] main
>>>   10.64%  xdpsock [kernel.vmlinux]    [k] clflush_cache_range
>>
>>
>> Oh, clflush_cache_range is being called!
>> Do your system use an IOMMU ?
>
>
> Whats the implication here. Should IOMMU be disabled?
> I'm asking because I do see a huge difference while running pktgen test for
> my performance benchmarks, with and without intel_iommu.
>
>
> -Tushar

For the Intel parts the IOMMU can be expensive primarily for Tx, since
it should have minimal impact if the Rx pages are pinned/recycled. I
am assuming the same is true here for AF_XDP, Bjorn can correct me if
I am wrong.

Basically the IOMMU can make creating/destroying a DMA mapping really
expensive. The easiest way to work around it in the case of the Intel
IOMMU is to boot with "iommu=pt" which will create an identity mapping
for the host. The downside is though that you then have the entire
system accessible to the device unless a new mapping is created for it
by assigning it to a new IOMMU domain.

Thanks.

- Alex

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