netdev - Re: [PATCH v10 12/12] bpf: add sample for xdp forwarding and rewrite

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Date:	Wed, 3 Aug 2016 10:11:20 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	Brenden Blanco <bblanco@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Saeed Mahameed <saeedm@....mellanox.co.il>,
	Martin KaFai Lau <kafai@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Ari Saha <as754m@....com>, Or Gerlitz <gerlitz.or@...il.com>,
	john fastabend <john.fastabend@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Thomas Graf <tgraf@...g.ch>,
	Daniel Borkmann <daniel@...earbox.net>,
	Tariq Toukan <ttoukan.linux@...il.com>,
	Aaron Yue <haoxuany@...com>
Subject: Re: [PATCH v10 12/12] bpf: add sample for xdp forwarding and rewrite

On Wed, Aug 03, 2016 at 10:01:54AM -0700, Tom Herbert wrote:
> On Tue, Jul 19, 2016 at 12:16 PM, Brenden Blanco <bblanco@...mgrid.com> wrote:
> > Add a sample that rewrites and forwards packets out on the same
> > interface. Observed single core forwarding performance of ~10Mpps.
> >
> > Since the mlx4 driver under test recycles every single packet page, the
> > perf output shows almost exclusively just the ring management and bpf
> > program work. Slowdowns are likely occurring due to cache misses.
> >
> > Signed-off-by: Brenden Blanco <bblanco@...mgrid.com>
> > ---
> >  samples/bpf/Makefile    |   5 +++
> >  samples/bpf/xdp2_kern.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 119 insertions(+)
> >  create mode 100644 samples/bpf/xdp2_kern.c
> >
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index 0e4ab3a..d2d2b35 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -22,6 +22,7 @@ hostprogs-y += map_perf_test
> >  hostprogs-y += test_overhead
> >  hostprogs-y += test_cgrp2_array_pin
> >  hostprogs-y += xdp1
> > +hostprogs-y += xdp2
> >
> >  test_verifier-objs := test_verifier.o libbpf.o
> >  test_maps-objs := test_maps.o libbpf.o
> > @@ -44,6 +45,8 @@ map_perf_test-objs := bpf_load.o libbpf.o map_perf_test_user.o
> >  test_overhead-objs := bpf_load.o libbpf.o test_overhead_user.o
> >  test_cgrp2_array_pin-objs := libbpf.o test_cgrp2_array_pin.o
> >  xdp1-objs := bpf_load.o libbpf.o xdp1_user.o
> > +# reuse xdp1 source intentionally
> > +xdp2-objs := bpf_load.o libbpf.o xdp1_user.o
> >
> >  # Tell kbuild to always build the programs
> >  always := $(hostprogs-y)
> > @@ -67,6 +70,7 @@ always += test_overhead_kprobe_kern.o
> >  always += parse_varlen.o parse_simple.o parse_ldabs.o
> >  always += test_cgrp2_tc_kern.o
> >  always += xdp1_kern.o
> > +always += xdp2_kern.o
> >
> >  HOSTCFLAGS += -I$(objtree)/usr/include
> >
> > @@ -88,6 +92,7 @@ HOSTLOADLIBES_spintest += -lelf
> >  HOSTLOADLIBES_map_perf_test += -lelf -lrt
> >  HOSTLOADLIBES_test_overhead += -lelf -lrt
> >  HOSTLOADLIBES_xdp1 += -lelf
> > +HOSTLOADLIBES_xdp2 += -lelf
> >
> >  # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
> >  #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> > diff --git a/samples/bpf/xdp2_kern.c b/samples/bpf/xdp2_kern.c
> > new file mode 100644
> > index 0000000..38fe7e1
> > --- /dev/null
> > +++ b/samples/bpf/xdp2_kern.c
> > @@ -0,0 +1,114 @@
> > +/* Copyright (c) 2016 PLUMgrid
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of version 2 of the GNU General Public
> > + * License as published by the Free Software Foundation.
> > + */
> > +#define KBUILD_MODNAME "foo"
> > +#include <uapi/linux/bpf.h>
> > +#include <linux/in.h>
> > +#include <linux/if_ether.h>
> > +#include <linux/if_packet.h>
> > +#include <linux/if_vlan.h>
> > +#include <linux/ip.h>
> > +#include <linux/ipv6.h>
> > +#include "bpf_helpers.h"
> > +
> > +struct bpf_map_def SEC("maps") dropcnt = {
> > +       .type = BPF_MAP_TYPE_PERCPU_ARRAY,
> > +       .key_size = sizeof(u32),
> > +       .value_size = sizeof(long),
> > +       .max_entries = 256,
> > +};
> > +
> > +static void swap_src_dst_mac(void *data)
> > +{
> > +       unsigned short *p = data;
> > +       unsigned short dst[3];
> > +
> > +       dst[0] = p[0];
> > +       dst[1] = p[1];
> > +       dst[2] = p[2];
> > +       p[0] = p[3];
> > +       p[1] = p[4];
> > +       p[2] = p[5];
> > +       p[3] = dst[0];
> > +       p[4] = dst[1];
> > +       p[5] = dst[2];
> > +}
> > +
> > +static int parse_ipv4(void *data, u64 nh_off, void *data_end)
> > +{
> > +       struct iphdr *iph = data + nh_off;
> > +
> > +       if (iph + 1 > data_end)
> > +               return 0;
> > +       return iph->protocol;
> > +}
> > +
> > +static int parse_ipv6(void *data, u64 nh_off, void *data_end)
> > +{
> > +       struct ipv6hdr *ip6h = data + nh_off;
> > +
> > +       if (ip6h + 1 > data_end)
> > +               return 0;
> > +       return ip6h->nexthdr;
> > +}
> > +
> > +SEC("xdp1")
> > +int xdp_prog1(struct xdp_md *ctx)
> > +{
> > +       void *data_end = (void *)(long)ctx->data_end;
> > +       void *data = (void *)(long)ctx->data;
> 
> Brendan,
> 
> It seems that the cast to long here is done because data_end and data
> are u32s in xdp_md. So the effect is that we are upcasting a
> thirty-bit integer into a sixty-four bit pointer (in fact without the
> cast we see compiler warnings). I don't understand how this can be
> correct. Can you shed some light on this?

please see:
http://lists.iovisor.org/pipermail/iovisor-dev/2016-August/000355.html