Date:   Sun, 8 Mar 2020 22:57:59 -0700
From:   Yonghong Song <yhs@...com>
To:     Song Liu <songliubraving@...com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
CC:     <quentin@...valent.com>, <kernel-team@...com>, <ast@...nel.org>,
        <daniel@...earbox.net>, <arnaldo.melo@...il.com>,
        <jolsa@...nel.org>
Subject: Re: [PATCH v5 bpf-next 1/4] bpftool: introduce "prog profile" command



On 3/6/20 4:17 PM, Song Liu wrote:
> With fentry/fexit programs, it is possible to profile BPF program with
> hardware counters. Introduce bpftool "prog profile", which measures key
> metrics of a BPF program.
> 
> bpftool prog profile command creates per-cpu perf events. Then it attaches
> fentry/fexit programs to the target BPF program. The fentry program saves
> perf event value to a map. The fexit program reads the perf event again,
> and calculates the difference, which is the instructions/cycles used by
> the target program.
> 
> Example input and output:
> 
>    ./bpftool prog profile id 337 duration 3 cycles instructions llc_misses
> 
>          4228 run_cnt
>       3403698 cycles                                              (84.08%)
>       3525294 instructions   #  1.04 insn per cycle               (84.05%)
>            13 llc_misses     #  3.69 LLC misses per million isns  (83.50%)
> 
> This command measures cycles and instructions for BPF program with id
> 337 for 3 seconds. The program has triggered 4228 times. The rest of the
> output is similar to perf-stat. In this example, the counters were only
> counting ~84% of the time because of time multiplexing of perf counters.
> 
> Note that, this approach measures cycles and instructions in very small
> increments. So the fentry/fexit programs introduce noticeable errors to
> the measurement results.
> 
> The fentry/fexit programs are generated with BPF skeletons. Therefore, we
> build bpftool twice. The first time _bpftool is built without skeletons.
> Then, _bpftool is used to generate the skeletons. The second time, bpftool
> is built with skeletons.
> 
> Reviewed-by: Quentin Monnet <quentin@...valent.com>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>   tools/bpf/bpftool/Makefile                |  18 +
>   tools/bpf/bpftool/prog.c                  | 424 +++++++++++++++++++++-
>   tools/bpf/bpftool/skeleton/profiler.bpf.c | 171 +++++++++
>   tools/bpf/bpftool/skeleton/profiler.h     |  47 +++
>   tools/scripts/Makefile.include            |   1 +
>   5 files changed, 660 insertions(+), 1 deletion(-)
>   create mode 100644 tools/bpf/bpftool/skeleton/profiler.bpf.c
>   create mode 100644 tools/bpf/bpftool/skeleton/profiler.h

[...]

> diff --git a/tools/bpf/bpftool/skeleton/profiler.bpf.c b/tools/bpf/bpftool/skeleton/profiler.bpf.c
> new file mode 100644
> index 000000000000..20594ccb393d
> --- /dev/null
> +++ b/tools/bpf/bpftool/skeleton/profiler.bpf.c
> @@ -0,0 +1,171 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2020 Facebook
> +#include "profiler.h"
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#define ___bpf_concat(a, b) a ## b
> +#define ___bpf_apply(fn, n) ___bpf_concat(fn, n)
> +#define ___bpf_nth(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, N, ...) N
> +#define ___bpf_narg(...) \
> +	___bpf_nth(_, ##__VA_ARGS__, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
> +#define ___bpf_empty(...) \
> +	___bpf_nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
> +
> +#define ___bpf_ctx_cast0() ctx
> +#define ___bpf_ctx_cast1(x) ___bpf_ctx_cast0(), (void *)ctx[0]
> +#define ___bpf_ctx_cast2(x, args...) ___bpf_ctx_cast1(args), (void *)ctx[1]
> +#define ___bpf_ctx_cast3(x, args...) ___bpf_ctx_cast2(args), (void *)ctx[2]
> +#define ___bpf_ctx_cast4(x, args...) ___bpf_ctx_cast3(args), (void *)ctx[3]
> +#define ___bpf_ctx_cast5(x, args...) ___bpf_ctx_cast4(args), (void *)ctx[4]
> +#define ___bpf_ctx_cast6(x, args...) ___bpf_ctx_cast5(args), (void *)ctx[5]
> +#define ___bpf_ctx_cast7(x, args...) ___bpf_ctx_cast6(args), (void *)ctx[6]
> +#define ___bpf_ctx_cast8(x, args...) ___bpf_ctx_cast7(args), (void *)ctx[7]
> +#define ___bpf_ctx_cast9(x, args...) ___bpf_ctx_cast8(args), (void *)ctx[8]
> +#define ___bpf_ctx_cast10(x, args...) ___bpf_ctx_cast9(args), (void *)ctx[9]
> +#define ___bpf_ctx_cast11(x, args...) ___bpf_ctx_cast10(args), (void *)ctx[10]
> +#define ___bpf_ctx_cast12(x, args...) ___bpf_ctx_cast11(args), (void *)ctx[11]
> +#define ___bpf_ctx_cast(args...) \
> +	___bpf_apply(___bpf_ctx_cast, ___bpf_narg(args))(args)
> +
> +/*
> + * BPF_PROG is a convenience wrapper for generic tp_btf/fentry/fexit and
> + * similar kinds of BPF programs, that accept input arguments as a single
> + * pointer to untyped u64 array, where each u64 can actually be a typed
> + * pointer or integer of different size. Instead of requring user to write
> + * manual casts and work with array elements by index, BPF_PROG macro
> + * allows user to declare a list of named and typed input arguments in the
> + * same syntax as for normal C function. All the casting is hidden and
> + * performed transparently, while user code can just assume working with
> + * function arguments of specified type and name.
> + *
> + * Original raw context argument is preserved as well as 'ctx' argument.
> + * This is useful when using BPF helpers that expect original context
> + * as one of the parameters (e.g., for bpf_perf_event_output()).
> + */
> +#define BPF_PROG(name, args...)						    \
> +name(unsigned long long *ctx);						    \
> +static __always_inline typeof(name(0))					    \
> +____##name(unsigned long long *ctx, ##args);				    \
> +typeof(name(0)) name(unsigned long long *ctx)				    \
> +{									    \
> +	_Pragma("GCC diagnostic push")					    \
> +	_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")		    \
> +	return ____##name(___bpf_ctx_cast(args));			    \
> +	_Pragma("GCC diagnostic pop")					    \
> +}									    \
> +static __always_inline typeof(name(0))					    \
> +____##name(unsigned long long *ctx, ##args)


The above change has merged into tools/lib/bpf/bpf_tracing.h.
You can remove them by just including "bpf/bpf_tracing.h"?

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