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Date: Thu, 13 Feb 2020 21:55:04 +0000
From: Song Liu <songliubraving@...com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
CC: Networking <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
Kernel Team <Kernel-team@...com>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [RFC bpf-next 3/4] bpftool: introduce "prog profile" command
> On Feb 13, 2020, at 1:50 PM, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Song Liu <songliubraving@...com> writes:
>
>> 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 20 id 810 cycles instructions
>> cycles: duration 20 run_cnt 1368 miss_cnt 665
>> counter 503377 enabled 668202 running 351857
>> instructions: duration 20 run_cnt 1368 miss_cnt 707
>> counter 398625 enabled 502330 running 272014
>>
>> This command measures cycles and instructions for BPF program with id
>> 810 for 20 seconds. The program has triggered 1368 times. cycles was not
>> measured in 665 out of these runs, because of perf event multiplexing
>> (some perf commands are running in the background). In these runs, the BPF
>> program consumed 503377 cycles. The perf_event enabled and running time
>> are 668202 and 351857 respectively.
>>
>> Note that, this approach measures cycles and instructions in very small
>> increments. So the fentry/fexit programs introduce noticable errors to
>> the measurement results.
>>
>> The fentry/fexit programs are generated with BPF skeleton. Currently,
>> generation of the skeleton requires some manual steps.
>>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> tools/bpf/bpftool/profiler.skel.h | 820 ++++++++++++++++++++++
>> tools/bpf/bpftool/prog.c | 387 +++++++++-
>> tools/bpf/bpftool/skeleton/README | 3 +
>> tools/bpf/bpftool/skeleton/profiler.bpf.c | 185 +++++
>> tools/bpf/bpftool/skeleton/profiler.h | 47 ++
>> 5 files changed, 1441 insertions(+), 1 deletion(-)
>> create mode 100644 tools/bpf/bpftool/profiler.skel.h
>> create mode 100644 tools/bpf/bpftool/skeleton/README
>> 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/profiler.skel.h b/tools/bpf/bpftool/profiler.skel.h
>> new file mode 100644
>> index 000000000000..10e99989c03e
>> --- /dev/null
>> +++ b/tools/bpf/bpftool/profiler.skel.h
>> @@ -0,0 +1,820 @@
>> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
>> +
>> +/* THIS FILE IS AUTOGENERATED! */
>> +#ifndef __PROFILER_BPF_SKEL_H__
>> +#define __PROFILER_BPF_SKEL_H__
>> +
>> +#include <stdlib.h>
>> +#include <bpf/libbpf.h>
>> +
>> +struct profiler_bpf {
>> + struct bpf_object_skeleton *skeleton;
>> + struct bpf_object *obj;
>> + struct {
>> + struct bpf_map *events;
>> + struct bpf_map *fentry_readings;
>> + struct bpf_map *accum_readings;
>> + struct bpf_map *counts;
>> + struct bpf_map *miss_counts;
>> + struct bpf_map *rodata;
>> + } maps;
>> + struct {
>> + struct bpf_program *fentry_XXX;
>> + struct bpf_program *fexit_XXX;
>> + } progs;
>> + struct {
>> + struct bpf_link *fentry_XXX;
>> + struct bpf_link *fexit_XXX;
>> + } links;
>> + struct profiler_bpf__rodata {
>> + __u32 num_cpu;
>> + __u32 num_metric;
>> + } *rodata;
>> +};
>> +
>> +static void
>> +profiler_bpf__destroy(struct profiler_bpf *obj)
>> +{
>> + if (!obj)
>> + return;
>> + if (obj->skeleton)
>> + bpf_object__destroy_skeleton(obj->skeleton);
>> + free(obj);
>> +}
>> +
>> +static inline int
>> +profiler_bpf__create_skeleton(struct profiler_bpf *obj);
>> +
>> +static inline struct profiler_bpf *
>> +profiler_bpf__open_opts(const struct bpf_object_open_opts *opts)
>> +{
>> + struct profiler_bpf *obj;
>> +
>> + obj = (typeof(obj))calloc(1, sizeof(*obj));
>> + if (!obj)
>> + return NULL;
>> + if (profiler_bpf__create_skeleton(obj))
>> + goto err;
>> + if (bpf_object__open_skeleton(obj->skeleton, opts))
>> + goto err;
>> +
>> + return obj;
>> +err:
>> + profiler_bpf__destroy(obj);
>> + return NULL;
>> +}
>> +
>> +static inline struct profiler_bpf *
>> +profiler_bpf__open(void)
>> +{
>> + return profiler_bpf__open_opts(NULL);
>> +}
>> +
>> +static inline int
>> +profiler_bpf__load(struct profiler_bpf *obj)
>> +{
>> + return bpf_object__load_skeleton(obj->skeleton);
>> +}
>> +
>> +static inline struct profiler_bpf *
>> +profiler_bpf__open_and_load(void)
>> +{
>> + struct profiler_bpf *obj;
>> +
>> + obj = profiler_bpf__open();
>> + if (!obj)
>> + return NULL;
>> + if (profiler_bpf__load(obj)) {
>> + profiler_bpf__destroy(obj);
>> + return NULL;
>> + }
>> + return obj;
>> +}
>> +
>> +static inline int
>> +profiler_bpf__attach(struct profiler_bpf *obj)
>> +{
>> + return bpf_object__attach_skeleton(obj->skeleton);
>> +}
>> +
>> +static inline void
>> +profiler_bpf__detach(struct profiler_bpf *obj)
>> +{
>> + return bpf_object__detach_skeleton(obj->skeleton);
>> +}
>> +
>> +static inline int
>> +profiler_bpf__create_skeleton(struct profiler_bpf *obj)
>> +{
>> + struct bpf_object_skeleton *s;
>> +
>> + s = (typeof(s))calloc(1, sizeof(*s));
>> + if (!s)
>> + return -1;
>> + obj->skeleton = s;
>> +
>> + s->sz = sizeof(*s);
>> + s->name = "profiler_bpf";
>> + s->obj = &obj->obj;
>> +
>> + /* maps */
>> + s->map_cnt = 6;
>> + s->map_skel_sz = sizeof(*s->maps);
>> + s->maps = (typeof(s->maps))calloc(s->map_cnt, s->map_skel_sz);
>> + if (!s->maps)
>> + goto err;
>> +
>> + s->maps[0].name = "events";
>> + s->maps[0].map = &obj->maps.events;
>> +
>> + s->maps[1].name = "fentry_readings";
>> + s->maps[1].map = &obj->maps.fentry_readings;
>> +
>> + s->maps[2].name = "accum_readings";
>> + s->maps[2].map = &obj->maps.accum_readings;
>> +
>> + s->maps[3].name = "counts";
>> + s->maps[3].map = &obj->maps.counts;
>> +
>> + s->maps[4].name = "miss_counts";
>> + s->maps[4].map = &obj->maps.miss_counts;
>> +
>> + s->maps[5].name = "profiler.rodata";
>> + s->maps[5].map = &obj->maps.rodata;
>> + s->maps[5].mmaped = (void **)&obj->rodata;
>> +
>> + /* programs */
>> + s->prog_cnt = 2;
>> + s->prog_skel_sz = sizeof(*s->progs);
>> + s->progs = (typeof(s->progs))calloc(s->prog_cnt, s->prog_skel_sz);
>> + if (!s->progs)
>> + goto err;
>> +
>> + s->progs[0].name = "fentry_XXX";
>> + s->progs[0].prog = &obj->progs.fentry_XXX;
>> + s->progs[0].link = &obj->links.fentry_XXX;
>> +
>> + s->progs[1].name = "fexit_XXX";
>> + s->progs[1].prog = &obj->progs.fexit_XXX;
>> + s->progs[1].link = &obj->links.fexit_XXX;
>> +
>> + s->data_sz = 18256;
>> + s->data = (void *)"\
>> +\x7f\x45\x4c\x46\x02\x01\x01\0\0\0\0\0\0\0\0\0\x01\0\xf7\0\x01\0\0\0\0\0\0\0\0\
>
> Holy binary blob, Batman! :)
>
> What is this blob, exactly? The bytecode output of a precompiled
> program?
It is the skeleton compiled from profiler.bpf.c. Please refer to
the README file for step to generate it.
In long term, we should include the generation of this blob in the
make process. But for RFC, I kept it simple for now. :)
Thanks,
Song
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