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add submodule from libbpf-bootstrap

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yunwei37
2023-05-07 00:59:20 +08:00
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src/12-profile/README.md
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@@ -1,83 +1,89 @@
## eBPF 入门实践教程：编写 eBPF 程序 profile 进行性能分析
# eBPF 入门实践教程：编写 eBPF 程序 profile 进行性能分析
### 背景
## 背景
`profile` 是一款用户追踪程序执行调用流程的工具，类似于perf中的 -g 指令。但是相较于perf而言，
`profile`的功能更为细化，它可以选择用户需要追踪的层面，比如在用户态层面进行追踪，或是在内核态进行追踪。
### 实现原理
## 实现原理
`profile` 的实现依赖于linux中的perf_event。在注入ebpf程序前，`profile` 工具会先将 perf_event
`profile` 的实现依赖于linux中的perf_event。在注入ebpf程序前，`profile` 工具会先将 perf_event
注册好。
```c
static int open_and_attach_perf_event(int freq, struct bpf_program *prog,
struct bpf_link *links[])
struct bpf_link *links[])
{
struct perf_event_attr attr = {
.type = PERF_TYPE_SOFTWARE,
.freq = env.freq,
.sample_freq = env.sample_freq,
.config = PERF_COUNT_SW_CPU_CLOCK,
};
int i, fd;
struct perf_event_attr attr = {
.type = PERF_TYPE_SOFTWARE,
.freq = env.freq,
.sample_freq = env.sample_freq,
.config = PERF_COUNT_SW_CPU_CLOCK,
};
int i, fd;
for (i = 0; i < nr_cpus; i++) {
if (env.cpu != -1 && env.cpu != i)
continue;
for (i = 0; i < nr_cpus; i++) {
if (env.cpu != -1 && env.cpu != i)
continue;
fd = syscall(__NR_perf_event_open, &attr, -1, i, -1, 0);
if (fd < 0) {
/* Ignore CPU that is offline */
if (errno == ENODEV)
continue;
fprintf(stderr, "failed to init perf sampling: %s\n",
strerror(errno));
return -1;
}
links[i] = bpf_program__attach_perf_event(prog, fd);
if (!links[i]) {
fprintf(stderr, "failed to attach perf event on cpu: "
"%d\n", i);
links[i] = NULL;
close(fd);
return -1;
}
}
fd = syscall(__NR_perf_event_open, &attr, -1, i, -1, 0);
if (fd < 0) {
/* Ignore CPU that is offline */
if (errno == ENODEV)
continue;
fprintf(stderr, "failed to init perf sampling: %s\n",
strerror(errno));
return -1;
}
links[i] = bpf_program__attach_perf_event(prog, fd);
if (!links[i]) {
fprintf(stderr, "failed to attach perf event on cpu: "
"%d\n", i);
links[i] = NULL;
close(fd);
return -1;
}
}
return 0;
return 0;
}
```
其ebpf程序实现逻辑是对程序的堆栈进行定时采样，从而捕获程序的执行流程。
```c
SEC("perf_event")
int profile(void *ctx)
{
int pid = bpf_get_current_pid_tgid() >> 32;
int cpu_id = bpf_get_smp_processor_id();
struct stacktrace_event *event;
int cp;
int pid = bpf_get_current_pid_tgid() >> 32;
int cpu_id = bpf_get_smp_processor_id();
struct stacktrace_event *event;
int cp;
event = bpf_ringbuf_reserve(&events, sizeof(*event), 0);
if (!event)
return 1;
event = bpf_ringbuf_reserve(&events, sizeof(*event), 0);
if (!event)
return 1;
event->pid = pid;
event->cpu_id = cpu_id;
event->pid = pid;
event->cpu_id = cpu_id;
if (bpf_get_current_comm(event->comm, sizeof(event->comm)))
event->comm[0] = 0;
if (bpf_get_current_comm(event->comm, sizeof(event->comm)))
event->comm[0] = 0;
event->kstack_sz = bpf_get_stack(ctx, event->kstack, sizeof(event->kstack), 0);
event->kstack_sz = bpf_get_stack(ctx, event->kstack, sizeof(event->kstack), 0);
event->ustack_sz = bpf_get_stack(ctx, event->ustack, sizeof(event->ustack), BPF_F_USER_STACK);
event->ustack_sz = bpf_get_stack(ctx, event->ustack, sizeof(event->ustack), BPF_F_USER_STACK);
bpf_ringbuf_submit(event, 0);
bpf_ringbuf_submit(event, 0);
return 0;
return 0;
}
```
通过这种方式，它可以根据用户指令，简单的决定追踪用户态层面的执行流程或是内核态层面的执行流程。
### 编译运行
## 编译运行
```console
$ git clone https://github.com/libbpf/libbpf-bootstrap.git --recurse-submodules
$ cd examples/c
@@ -105,4 +111,5 @@ Userspace:
```
### 总结
`profile` 实现了对程序执行流程的分析，在debug等操作中可以极大的帮助开发者提高效率。