netdev - Re: [PATCH bpf-next v2 2/6] xdp: introduce xdp

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Date:   Sun, 24 Nov 2019 07:56:49 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: Re: [PATCH bpf-next v2 2/6] xdp: introduce xdp_call

On Sun, 24 Nov 2019 at 02:59, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, Nov 23, 2019 at 08:12:21AM +0100, Björn Töpel wrote:
> > From: Björn Töpel <bjorn.topel@...el.com>
> >
> > The xdp_call.h header wraps a more user-friendly API around the BPF
> > dispatcher. A user adds a trampoline/XDP caller using the
> > DEFINE_XDP_CALL macro, and updates the BPF dispatcher via
> > xdp_call_update(). The actual dispatch is done via xdp_call().
> >
> > Note that xdp_call() is only supported for builtin drivers. Module
> > builds will fallback to bpf_prog_run_xdp().
> >
> > The next patch will show-case how the i40e driver uses xdp_call.
> >
> > Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> > ---
> >  include/linux/xdp_call.h | 66 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 66 insertions(+)
> >  create mode 100644 include/linux/xdp_call.h
> >
> > diff --git a/include/linux/xdp_call.h b/include/linux/xdp_call.h
> > new file mode 100644
> > index 000000000000..69b2d325a787
> > --- /dev/null
> > +++ b/include/linux/xdp_call.h
> > @@ -0,0 +1,66 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/* Copyright(c) 2019 Intel Corporation. */
> > +#ifndef _LINUX_XDP_CALL_H
> > +#define _LINUX_XDP_CALL_H
> > +
> > +#include <linux/filter.h>
> > +
> > +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_RETPOLINE) && !defined(MODULE)
> > +
> > +void bpf_dispatcher_change_prog(void *func, struct bpf_prog *from,
> > +                             struct bpf_prog *to);
> > +
> > +#define XDP_CALL_TRAMP(name) ____xdp_call_##name##_tramp
> > +
> > +#define DEFINE_XDP_CALL(name)                                                \
> > +     unsigned int XDP_CALL_TRAMP(name)(                              \
> > +             const void *xdp_ctx,                                    \
> > +             const struct bpf_insn *insnsi,                          \
> > +             unsigned int (*bpf_func)(const void *,                  \
> > +                                      const struct bpf_insn *))      \
> > +     {                                                               \
> > +             return bpf_func(xdp_ctx, insnsi);                       \
> > +     }
> > +
> > +#define DECLARE_XDP_CALL(name)                                               \
> > +     unsigned int XDP_CALL_TRAMP(name)(                              \
> > +             const void *xdp_ctx,                                    \
> > +             const struct bpf_insn *insnsi,                          \
> > +             unsigned int (*bpf_func)(const void *,                  \
> > +                                      const struct bpf_insn *))
> > +
> > +#define xdp_call_run(name, prog, ctx) ({                             \
> > +     u32 ret;                                                        \
> > +     cant_sleep();                                                   \
> > +     if (static_branch_unlikely(&bpf_stats_enabled_key)) {           \
> > +             struct bpf_prog_stats *stats;                           \
> > +             u64 start = sched_clock();                              \
> > +             ret = XDP_CALL_TRAMP(name)(ctx,                         \
> > +                                        (prog)->insnsi,              \
> > +                                        (prog)->bpf_func);           \
> > +             stats = this_cpu_ptr((prog)->aux->stats);               \
> > +             u64_stats_update_begin(&stats->syncp);                  \
> > +             stats->cnt++;                                           \
> > +             stats->nsecs += sched_clock() - start;                  \
> > +             u64_stats_update_end(&stats->syncp);                    \
> > +     } else {                                                        \
> > +             ret = XDP_CALL_TRAMP(name)(ctx,                         \
> > +                                        (prog)->insnsi,              \
> > +                                        (prog)->bpf_func);           \
> > +     }                                                               \
> > +     ret; })
>
> I cannot help but wonder whether it's possible to avoid copy-paste from
> BPF_PROG_RUN().
> At least could you place this new macro right next to BPF_PROG_RUN?
> If it's in a different file eventually they may diverge.
>

Yeah, I'll take a stab at that!


Thanks,
Björn