From: Yonghong Song <yhs@fb.com>
To: Song Liu <songliubraving@fb.com>, <netdev@vger.kernel.org>,
<bpf@vger.kernel.org>
Cc: <quentin@isovalent.com>, <kernel-team@fb.com>, <ast@kernel.org>,
<daniel@iogearbox.net>, <arnaldo.melo@gmail.com>,
<jolsa@kernel.org>
Subject: Re: [PATCH v5 bpf-next 1/4] bpftool: introduce "prog profile" command
Date: Sun, 8 Mar 2020 22:57:59 -0700 [thread overview]
Message-ID: <4fe1d235-21a5-0463-3079-ca1852b3510d@fb.com> (raw)
In-Reply-To: <20200307001713.3559880-2-songliubraving@fb.com>
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@isovalent.com>
> Signed-off-by: Song Liu <songliubraving@fb.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"?
next prev parent reply other threads:[~2020-03-09 5:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-07 0:17 [PATCH v5 bpf-next 0/4] bpftool: introduce prog profile Song Liu
2020-03-07 0:17 ` [PATCH v5 bpf-next 1/4] bpftool: introduce "prog profile" command Song Liu
2020-03-09 5:57 ` Yonghong Song [this message]
2020-03-07 0:17 ` [PATCH v5 bpf-next 2/4] bpftool: Documentation for bpftool prog profile Song Liu
2020-03-07 0:17 ` [PATCH v5 bpf-next 3/4] ybpftool: bash completion for "bpftool prog profile" Song Liu
2020-03-07 0:17 ` [PATCH v5 bpf-next 4/4] bpftool: fix typo in bash-completion Song Liu
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