Re: [PATCH 4/5] perf ftrace: Add -b/--use-bpf option for latency subcommand

[Athira Rajeev]

> On 30-Nov-2021, at 4:48 AM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> 
> The -b/--use-bpf option is to use BPF to get latency info of kernel
> functions.  It'd have better performance impact and I observed that
> latency of same function is smaller than before when using BPF.
> 
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
> tools/perf/Makefile.perf                    |   2 +-
> tools/perf/builtin-ftrace.c                 | 156 +++++++++++---------
> tools/perf/util/Build                       |   1 +
> tools/perf/util/bpf_ftrace.c                | 113 ++++++++++++++
> tools/perf/util/bpf_skel/func_latency.bpf.c |  92 ++++++++++++
> tools/perf/util/ftrace.h                    |  81 ++++++++++
> 6 files changed, 378 insertions(+), 67 deletions(-)
> create mode 100644 tools/perf/util/bpf_ftrace.c
> create mode 100644 tools/perf/util/bpf_skel/func_latency.bpf.c
> create mode 100644 tools/perf/util/ftrace.h
> 
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 80522bcfafe0..a861b92ac6f9 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -1041,7 +1041,7 @@ SKEL_OUT := $(abspath $(OUTPUT)util/bpf_skel)
> SKEL_TMP_OUT := $(abspath $(SKEL_OUT)/.tmp)
> SKELETONS := $(SKEL_OUT)/bpf_prog_profiler.skel.h
> SKELETONS += $(SKEL_OUT)/bperf_leader.skel.h $(SKEL_OUT)/bperf_follower.skel.h
> -SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h
> +SKELETONS += $(SKEL_OUT)/bperf_cgroup.skel.h $(SKEL_OUT)/func_latency.skel.h
> 
> $(SKEL_TMP_OUT) $(LIBBPF_OUTPUT):
> 	$(Q)$(MKDIR) -p $@
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 8fd3c9c44c69..cde1e87032a1 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -30,36 +30,12 @@
> #include "strfilter.h"
> #include "util/cap.h"
> #include "util/config.h"
> +#include "util/ftrace.h"
> #include "util/units.h"
> #include "util/parse-sublevel-options.h"
> 
> #define DEFAULT_TRACER  "function_graph"
> 
> -struct perf_ftrace {
> -	struct evlist		*evlist;
> -	struct target		target;
> -	const char		*tracer;
> -	struct list_head	filters;
> -	struct list_head	notrace;
> -	struct list_head	graph_funcs;
> -	struct list_head	nograph_funcs;
> -	int			graph_depth;
> -	unsigned long		percpu_buffer_size;
> -	bool			inherit;
> -	int			func_stack_trace;
> -	int			func_irq_info;
> -	int			graph_nosleep_time;
> -	int			graph_noirqs;
> -	int			graph_verbose;
> -	int			graph_thresh;
> -	unsigned int		initial_delay;
> -};
> -
> -struct filter_entry {
> -	struct list_head	list;
> -	char			name[];
> -};
> -
> static volatile int workload_exec_errno;
> static bool done;
> 
> @@ -704,8 +680,6 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace)
> 	return (done && !workload_exec_errno) ? 0 : -1;
> }
> 
> -#define NUM_BUCKET  22  /* 20 + 2 (for outliers in both direction) */
> -
> static void make_histogram(int buckets[], char *buf, size_t len, char *linebuf)
> {
> 	char *p, *q;
> @@ -816,69 +790,116 @@ static void display_histogram(int buckets[])
> 
> }
> 
> -static int __cmd_latency(struct perf_ftrace *ftrace)
> +static int prepare_func_latency(struct perf_ftrace *ftrace)
> {
> 	char *trace_file;
> -	int trace_fd;
> -	char buf[4096];
> -	char line[256];
> -	struct pollfd pollfd = {
> -		.events = POLLIN,
> -	};
> -	int buckets[NUM_BUCKET] = { };
> +	int fd;
> 
> -	if (!(perf_cap__capable(CAP_PERFMON) ||
> -	      perf_cap__capable(CAP_SYS_ADMIN))) {
> -		pr_err("ftrace only works for %s!\n",
> -#ifdef HAVE_LIBCAP_SUPPORT
> -		"users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> -#else
> -		"root"
> -#endif
> -		);
> -		return -1;
> -	}
> +	if (ftrace->target.use_bpf)
> +		return perf_ftrace__latency_prepare_bpf(ftrace);
> 
> 	if (reset_tracing_files(ftrace) < 0) {
> 		pr_err("failed to reset ftrace\n");
> -		goto out;
> +		return -1;
> 	}
> 
> 	/* reset ftrace buffer */
> 	if (write_tracing_file("trace", "0") < 0)
> -		goto out;
> +		return -1;
> 
> 	if (set_tracing_options(ftrace) < 0)
> -		goto out_reset;
> +		return -1;
> 
> 	/* force to use the function_graph tracer to track duration */
> 	if (write_tracing_file("current_tracer", "function_graph") < 0) {
> 		pr_err("failed to set current_tracer to function_graph\n");
> -		goto out_reset;
> +		return -1;
> 	}
> 
> 	trace_file = get_tracing_file("trace_pipe");
> 	if (!trace_file) {
> 		pr_err("failed to open trace_pipe\n");
> -		goto out_reset;
> +		return -1;
> 	}
> 
> -	trace_fd = open(trace_file, O_RDONLY);
> +	fd = open(trace_file, O_RDONLY);
> +	if (fd < 0)
> +		pr_err("failed to open trace_pipe\n");
> 
> 	put_tracing_file(trace_file);
> +	return fd;
> +}
> 
> -	if (trace_fd < 0) {
> -		pr_err("failed to open trace_pipe\n");
> -		goto out_reset;
> +static int start_func_latency(struct perf_ftrace *ftrace)
> +{
> +	if (ftrace->target.use_bpf)
> +		return perf_ftrace__latency_start_bpf(ftrace);
> +
> +	if (write_tracing_file("tracing_on", "1") < 0) {
> +		pr_err("can't enable tracing\n");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
> +static int stop_func_latency(struct perf_ftrace *ftrace)
> +{
> +	if (ftrace->target.use_bpf)
> +		return perf_ftrace__latency_stop_bpf(ftrace);
> +
> +	write_tracing_file("tracing_on", "0");
> +	return 0;
> +}
> +
> +static int read_func_latency(struct perf_ftrace *ftrace, int buckets[])
> +{
> +	if (ftrace->target.use_bpf)
> +		return perf_ftrace__latency_read_bpf(ftrace, buckets);
> +
> +	return 0;
> +}
> +
> +static int cleanup_func_latency(struct perf_ftrace *ftrace)
> +{
> +	if (ftrace->target.use_bpf)
> +		return perf_ftrace__latency_cleanup_bpf(ftrace);
> +
> +	reset_tracing_files(ftrace);
> +	return 0;
> +}
> +
> +static int __cmd_latency(struct perf_ftrace *ftrace)
> +{
> +	int trace_fd;
> +	char buf[4096];
> +	char line[256];
> +	struct pollfd pollfd = {
> +		.events = POLLIN,
> +	};
> +	int buckets[NUM_BUCKET] = { };
> +
> +	if (!(perf_cap__capable(CAP_PERFMON) ||
> +	      perf_cap__capable(CAP_SYS_ADMIN))) {
> +		pr_err("ftrace only works for %s!\n",
> +#ifdef HAVE_LIBCAP_SUPPORT
> +		"users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> +#else
> +		"root"
> +#endif
> +		);
> +		return -1;
> 	}
> 
> +	trace_fd = prepare_func_latency(ftrace);
> +	if (trace_fd < 0)
> +		goto out;
> +
> 	fcntl(trace_fd, F_SETFL, O_NONBLOCK);
> 	pollfd.fd = trace_fd;
> 
> -	if (write_tracing_file("tracing_on", "1") < 0) {
> -		pr_err("can't enable tracing\n");
> -		goto out_close_fd;
> -	}
> +	if (start_func_latency(ftrace) < 0)
> +		goto out;
> 
> 	evlist__start_workload(ftrace->evlist);
> 
> @@ -896,29 +917,30 @@ static int __cmd_latency(struct perf_ftrace *ftrace)
> 		}
> 	}
> 
> -	write_tracing_file("tracing_on", "0");
> +	stop_func_latency(ftrace);
> 
> 	if (workload_exec_errno) {
> 		const char *emsg = str_error_r(workload_exec_errno, buf, sizeof(buf));
> 		pr_err("workload failed: %s\n", emsg);
> -		goto out_close_fd;
> +		goto out;
> 	}
> 
> 	/* read remaining buffer contents */
> -	while (true) {
> +	while (!ftrace->target.use_bpf) {
> 		int n = read(trace_fd, buf, sizeof(buf) - 1);
> 		if (n <= 0)
> 			break;
> 		make_histogram(buckets, buf, n, line);
> 	}
> 
> +	read_func_latency(ftrace, buckets);
> +
> 	display_histogram(buckets);
> 
> -out_close_fd:
> -	close(trace_fd);
> -out_reset:
> -	reset_tracing_files(ftrace);
> out:
> +	close(trace_fd);
> +	cleanup_func_latency(ftrace);
> +
> 	return (done && !workload_exec_errno) ? 0 : -1;
> }
> 
> @@ -1144,6 +1166,8 @@ int cmd_ftrace(int argc, const char **argv)
> 	const struct option latency_options[] = {
> 	OPT_CALLBACK('T', "trace-funcs", &ftrace.filters, "func",
> 		     "Show latency of given function", parse_filter_func),
> +	OPT_BOOLEAN('b', "use-bpf", &ftrace.target.use_bpf,
> +		    "Use BPF to measure function latency"),


Hi Namhyung,

Can this be inside BPF_SKEL check, similar to how we have “bpf-prog” and other options in builtin-stat.c ?

#ifdef HAVE_BPF_SKEL
<<OPT_BOOLEAN for use-bpf>>
#endif

Otherwise when using “-b” and if perf is not built with BPF_SKEL, we will just return in perf_ftrace__latency_prepare_bpf without any error messages.

Thanks
Athira
> 	OPT_PARENT(common_options),
> 	};
> 	const struct option *options = ftrace_options;
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index 2e5bfbb69960..294b12430d73 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -144,6 +144,7 @@ perf-$(CONFIG_LIBBPF) += bpf-loader.o
> perf-$(CONFIG_LIBBPF) += bpf_map.o
> perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter.o
> perf-$(CONFIG_PERF_BPF_SKEL) += bpf_counter_cgroup.o
> +perf-$(CONFIG_PERF_BPF_SKEL) += bpf_ftrace.o
> perf-$(CONFIG_BPF_PROLOGUE) += bpf-prologue.o
> perf-$(CONFIG_LIBELF) += symbol-elf.o
> perf-$(CONFIG_LIBELF) += probe-file.o
> diff --git a/tools/perf/util/bpf_ftrace.c b/tools/perf/util/bpf_ftrace.c
> new file mode 100644
> index 000000000000..1975a6fe73c9
> --- /dev/null
> +++ b/tools/perf/util/bpf_ftrace.c
> @@ -0,0 +1,113 @@
> +#include <stdio.h>
> +#include <fcntl.h>
> +#include <stdint.h>
> +#include <stdlib.h>
> +
> +#include <linux/err.h>
> +
> +#include "util/ftrace.h"
> +#include "util/debug.h"
> +#include "util/bpf_counter.h"
> +
> +#include "util/bpf_skel/func_latency.skel.h"
> +
> +static struct func_latency_bpf *skel;
> +
> +int perf_ftrace__latency_prepare_bpf(struct perf_ftrace *ftrace)
> +{
> +	int fd, err;
> +	struct filter_entry *func;
> +	struct bpf_link *begin_link, *end_link;
> +
> +	if (!list_is_singular(&ftrace->filters)) {
> +		pr_err("ERROR: %s target function(s).\n",
> +		       list_empty(&ftrace->filters) ? "No" : "Too many");
> +		return -1;
> +	}
> +
> +	func = list_first_entry(&ftrace->filters, struct filter_entry, list);
> +
> +	skel = func_latency_bpf__open();
> +	if (!skel) {
> +		pr_err("Failed to open func latency skeleton\n");
> +		return -1;
> +	}
> +
> +	set_max_rlimit();
> +
> +	err = func_latency_bpf__load(skel);
> +	if (err) {
> +		pr_err("Failed to load func latency skeleton\n");
> +		goto out;
> +	}
> +
> +	begin_link = bpf_program__attach_kprobe(skel->progs.func_begin,
> +						 false, func->name);
> +	if (IS_ERR(begin_link)) {
> +		pr_err("Failed to attach fentry program\n");
> +		err = PTR_ERR(begin_link);
> +		goto out;
> +	}
> +
> +	end_link = bpf_program__attach_kprobe(skel->progs.func_end,
> +					      true, func->name);
> +	if (IS_ERR(end_link)) {
> +		pr_err("Failed to attach fexit program\n");
> +		err = PTR_ERR(end_link);
> +		bpf_link__destroy(begin_link);
> +		goto out;
> +	}
> +
> +	/* XXX: we don't actually use this fd - just for poll() */
> +	return open("/dev/null", O_RDONLY);
> +
> +out:
> +	return err;
> +}
> +
> +int perf_ftrace__latency_start_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	skel->bss->enabled = 1;
> +	return 0;
> +}
> +
> +int perf_ftrace__latency_stop_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	skel->bss->enabled = 0;
> +	return 0;
> +}
> +
> +int perf_ftrace__latency_read_bpf(struct perf_ftrace *ftrace __maybe_unused,
> +				  int buckets[])
> +{
> +	int i, fd, err;
> +	u32 idx;
> +	u64 *hist;
> +	int ncpus = cpu__max_cpu();
> +
> +	fd = bpf_map__fd(skel->maps.latency);
> +
> +	hist = calloc(ncpus, sizeof(*hist));
> +	if (hist == NULL)
> +		return -ENOMEM;
> +
> +	for (idx = 0; idx < NUM_BUCKET; idx++) {
> +		err = bpf_map_lookup_elem(fd, &idx, hist);
> +		if (err) {
> +			buckets[idx] = 0;
> +			continue;
> +		}
> +
> +		for (i = 0; i < ncpus; i++)
> +			buckets[idx] += hist[i];
> +	}
> +
> +	free(hist);
> +	return 0;
> +}
> +
> +int perf_ftrace__latency_cleanup_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	func_latency_bpf__destroy(skel);
> +	return 0;
> +}
> diff --git a/tools/perf/util/bpf_skel/func_latency.bpf.c b/tools/perf/util/bpf_skel/func_latency.bpf.c
> new file mode 100644
> index 000000000000..d7d31cfeabf8
> --- /dev/null
> +++ b/tools/perf/util/bpf_skel/func_latency.bpf.c
> @@ -0,0 +1,92 @@
> +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +// Copyright (c) 2021 Google
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#define NUM_BUCKET  22
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(__u64));
> +	__uint(value_size, sizeof(__u64));
> +	__uint(max_entries, 10000);
> +} functime SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u8));
> +	__uint(max_entries, 1);
> +} cpu_filter SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u8));
> +	__uint(max_entries, 1);
> +} task_filter SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
> +	__uint(key_size, sizeof(__u32));
> +	__uint(value_size, sizeof(__u64));
> +	__uint(max_entries, NUM_BUCKET);
> +} latency SEC(".maps");
> +
> +
> +int enabled = 0;
> +
> +SEC("kprobe/func")
> +int BPF_PROG(func_begin)
> +{
> +	__u64 key, now;
> +
> +	if (!enabled)
> +		return 0;
> +
> +	key = bpf_get_current_pid_tgid();
> +	now = bpf_ktime_get_ns();
> +
> +	// overwrite timestamp for nested functions
> +	bpf_map_update_elem(&functime, &key, &now, BPF_ANY);
> +	return 0;
> +}
> +
> +SEC("kretprobe/func")
> +int BPF_PROG(func_end)
> +{
> +	__u64 tid;
> +	__u64 *start;
> +
> +	if (!enabled)
> +		return 0;
> +
> +	tid = bpf_get_current_pid_tgid();
> +
> +	start = bpf_map_lookup_elem(&functime, &tid);
> +	if (start) {
> +		__s64 delta = bpf_ktime_get_ns() - *start;
> +		__u32 key;
> +		__u64 *hist;
> +
> +		bpf_map_delete_elem(&functime, &tid);
> +
> +		if (delta < 0)
> +			return 0;
> +
> +		// calculate index using delta in usec
> +		for (key = 0; key < (NUM_BUCKET - 1); key++) {
> +			if (delta < ((1000UL) << key))
> +				break;
> +		}
> +
> +		hist = bpf_map_lookup_elem(&latency, &key);
> +		if (!hist)
> +			return 0;
> +
> +		*hist += 1;
> +	}
> +
> +	return 0;
> +}
> diff --git a/tools/perf/util/ftrace.h b/tools/perf/util/ftrace.h
> new file mode 100644
> index 000000000000..887f68a185f7
> --- /dev/null
> +++ b/tools/perf/util/ftrace.h
> @@ -0,0 +1,81 @@
> +#ifndef __PERF_FTRACE_H__
> +#define __PERF_FTRACE_H__
> +
> +#include <linux/list.h>
> +
> +#include "target.h"
> +
> +struct evlist;
> +
> +struct perf_ftrace {
> +	struct evlist		*evlist;
> +	struct target		target;
> +	const char		*tracer;
> +	struct list_head	filters;
> +	struct list_head	notrace;
> +	struct list_head	graph_funcs;
> +	struct list_head	nograph_funcs;
> +	unsigned long		percpu_buffer_size;
> +	bool			inherit;
> +	int			graph_depth;
> +	int			func_stack_trace;
> +	int			func_irq_info;
> +	int			graph_nosleep_time;
> +	int			graph_noirqs;
> +	int			graph_verbose;
> +	int			graph_thresh;
> +	unsigned int		initial_delay;
> +};
> +
> +struct filter_entry {
> +	struct list_head	list;
> +	char			name[];
> +};
> +
> +#define NUM_BUCKET  22  /* 20 + 2 (for outliers in both direction) */
> +
> +#ifdef HAVE_BPF_SKEL
> +
> +int perf_ftrace__latency_prepare_bpf(struct perf_ftrace *ftrace);
> +int perf_ftrace__latency_start_bpf(struct perf_ftrace *ftrace);
> +int perf_ftrace__latency_stop_bpf(struct perf_ftrace *ftrace);
> +int perf_ftrace__latency_read_bpf(struct perf_ftrace *ftrace,
> +				  int buckets[]);
> +int perf_ftrace__latency_cleanup_bpf(struct perf_ftrace *ftrace);
> +
> +#else  /* !HAVE_BPF_SKEL */
> +
> +static inline int
> +perf_ftrace__latency_prepare_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	return -1;
> +}
> +
> +static inline int
> +perf_ftrace__latency_start_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	return -1;
> +}
> +
> +static inline int
> +perf_ftrace__latency_stop_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	return -1;
> +}
> +
> +static inline int
> +perf_ftrace__latency_read_bpf(struct perf_ftrace *ftrace __maybe_unused,
> +			      int buckets[] __maybe_unused)
> +{
> +	return -1;
> +}
> +
> +static inline int
> +perf_ftrace__latency_cleanup_bpf(struct perf_ftrace *ftrace __maybe_unused)
> +{
> +	return -1;
> +}
> +
> +#endif  /* HAVE_BPF_SKEL */
> +
> +#endif  /* __PERF_FTRACE_H__ */
> -- 
> 2.34.0.rc2.393.gf8c9666880-goog
> 
>