Subject: Re: [PATCH bpf-next 7/8] samples/bpf: add sample program that periodically dumps TCP stats

From: Stanislav Fomichev <[email-masked]>
Date: Mon, 1 Jul 2019 17:31:56 -0700

On 07/01, Y Song wrote:
> On Mon, Jul 1, 2019 at 1:49 PM Stanislav Fomichev <[email-masked]> wrote:
> >
> > Uses new RTT callback to dump stats every second.
> >
> > $ mkdir -p /tmp/cgroupv2
> > $ mount -t cgroup2 none /tmp/cgroupv2
> > $ mkdir -p /tmp/cgroupv2/foo
> > $ echo $$ >> /tmp/cgroupv2/foo/cgroup.procs
> > $ bpftool prog load ./tcp_dumpstats_kern.o /sys/fs/bpf/tcp_prog
> > $ bpftool cgroup attach /tmp/cgroupv2/foo sock_ops pinned /sys/fs/bpf/tcp_prog
> > $ bpftool prog tracelog
> > $ # run neper/netperf/etc
> >
> > Used neper to compare performance with and without this program attached
> > and didn't see any noticeable performance impact.
> >
> > Sample output:
> >   <idle>-0     [015] ..s.  2074.128800: 0: dsack_dups=0 delivered=242526
> >   <idle>-0     [015] ..s.  2074.128808: 0: delivered_ce=0 icsk_retransmits=0
> >   <idle>-0     [015] ..s.  2075.130133: 0: dsack_dups=0 delivered=323599
> >   <idle>-0     [015] ..s.  2075.130138: 0: delivered_ce=0 icsk_retransmits=0
> >   <idle>-0     [005] .Ns.  2076.131440: 0: dsack_dups=0 delivered=404648
> >   <idle>-0     [005] .Ns.  2076.131447: 0: delivered_ce=0 icsk_retransmits=0
> >
> > Cc: Eric Dumazet <[email-masked]>
> > Cc: Priyaranjan Jha <[email-masked]>
> > Cc: Yuchung Cheng <[email-masked]>
> > Cc: Soheil Hassas Yeganeh <[email-masked]>
> > Signed-off-by: Stanislav Fomichev <[email-masked]>
> > ---
> >  samples/bpf/Makefile             |  1 +
> >  samples/bpf/tcp_dumpstats_kern.c | 65 ++++++++++++++++++++++++++++++++
> >  2 files changed, 66 insertions(+)
> >  create mode 100644 samples/bpf/tcp_dumpstats_kern.c
> 
> Currently, the bpf program into the repo. If we do not have another
> script to use
> this program for testing, the instructions in the commit message should be
> added to the bpf program as comments so people know what to do with this file
> without going through git commit message.
> 
> Is it possible to create a script to run with this bpf program?
There is a general instruction in samples/bpf/tcp_bpf.readme
with bpftool examples/etc. Should I just a comment at the top
of the BPF program to point people to that .readme file instead?

> >
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index 0917f8cf4fab..eaebbeead42f 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -154,6 +154,7 @@ always += tcp_iw_kern.o
> >  always += tcp_clamp_kern.o
> >  always += tcp_basertt_kern.o
> >  always += tcp_tos_reflect_kern.o
> > +always += tcp_dumpstats_kern.o
> >  always += xdp_redirect_kern.o
> >  always += xdp_redirect_map_kern.o
> >  always += xdp_redirect_cpu_kern.o
> > diff --git a/samples/bpf/tcp_dumpstats_kern.c b/samples/bpf/tcp_dumpstats_kern.c
> > new file mode 100644
> > index 000000000000..5d22bf61db65
> > --- /dev/null
> > +++ b/samples/bpf/tcp_dumpstats_kern.c
> > @@ -0,0 +1,65 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/bpf.h>
> > +
> > +#include "bpf_helpers.h"
> > +#include "bpf_endian.h"
> > +
> > +#define INTERVAL                       1000000000ULL
> > +
> > +int _version SEC("version") = 1;
> > +char _license[] SEC("license") = "GPL";
> > +
> > +struct {
> > +       __u32 type;
> > +       __u32 map_flags;
> > +       int *key;
> > +       __u64 *value;
> > +} bpf_next_dump SEC(".maps") = {
> > +       .type = BPF_MAP_TYPE_SK_STORAGE,
> > +       .map_flags = BPF_F_NO_PREALLOC,
> > +};
> > +
> > +SEC("sockops")
> > +int _sockops(struct bpf_sock_ops *ctx)
> > +{
> > +       struct bpf_tcp_sock *tcp_sk;
> > +       struct bpf_sock *sk;
> > +       __u64 *next_dump;
> > +       __u64 now;
> > +
> > +       switch (ctx->op) {
> > +       case BPF_SOCK_OPS_TCP_CONNECT_CB:
> > +               bpf_sock_ops_cb_flags_set(ctx, BPF_SOCK_OPS_RTT_CB_FLAG);
> > +               return 1;
> > +       case BPF_SOCK_OPS_RTT_CB:
> > +               break;
> > +       default:
> > +               return 1;
> > +       }
> > +
> > +       sk = ctx->sk;
> > +       if (!sk)
> > +               return 1;
> > +
> > +       next_dump = bpf_sk_storage_get(&bpf_next_dump, sk, 0,
> > +                                      BPF_SK_STORAGE_GET_F_CREATE);
> > +       if (!next_dump)
> > +               return 1;
> > +
> > +       now = bpf_ktime_get_ns();
> > +       if (now < *next_dump)
> > +               return 1;
> > +
> > +       tcp_sk = bpf_tcp_sock(sk);
> > +       if (!tcp_sk)
> > +               return 1;
> > +
> > +       *next_dump = now + INTERVAL;
> > +
> > +       bpf_printk("dsack_dups=%u delivered=%u\n",
> > +                  tcp_sk->dsack_dups, tcp_sk->delivered);
> > +       bpf_printk("delivered_ce=%u icsk_retransmits=%u\n",
> > +                  tcp_sk->delivered_ce, tcp_sk->icsk_retransmits);
> > +
> > +       return 1;
> > +}
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >