mirror of
https://github.com/eunomia-bpf/bpf-developer-tutorial.git
synced 2026-02-03 18:24:27 +08:00
104 lines
2.7 KiB
Markdown
104 lines
2.7 KiB
Markdown
## eBPF 入门实践教程：编写 eBPF 程序 profile 进行性能分析
|
||
|
||
### 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
|
||
|
||
`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 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;
|
||
|
||
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;
|
||
}
|
||
```
|
||
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 do_perf_event(struct bpf_perf_event_data *ctx)
|
||
{
|
||
__u64 id = bpf_get_current_pid_tgid();
|
||
__u32 pid = id >> 32;
|
||
__u32 tid = id;
|
||
__u64 *valp;
|
||
static const __u64 zero;
|
||
struct key_t key = {};
|
||
|
||
if (!include_idle && tid == 0)
|
||
return 0;
|
||
|
||
if (targ_pid != -1 && targ_pid != pid)
|
||
return 0;
|
||
if (targ_tid != -1 && targ_tid != tid)
|
||
return 0;
|
||
|
||
key.pid = pid;
|
||
bpf_get_current_comm(&key.name, sizeof(key.name));
|
||
|
||
if (user_stacks_only)
|
||
key.kern_stack_id = -1;
|
||
else
|
||
key.kern_stack_id = bpf_get_stackid(&ctx->regs, &stackmap, 0);
|
||
|
||
if (kernel_stacks_only)
|
||
key.user_stack_id = -1;
|
||
else
|
||
key.user_stack_id = bpf_get_stackid(&ctx->regs, &stackmap, BPF_F_USER_STACK);
|
||
|
||
if (key.kern_stack_id >= 0) {
|
||
// populate extras to fix the kernel stack
|
||
__u64 ip = PT_REGS_IP(&ctx->regs);
|
||
|
||
if (is_kernel_addr(ip)) {
|
||
key.kernel_ip = ip;
|
||
}
|
||
}
|
||
|
||
valp = bpf_map_lookup_or_try_init(&counts, &key, &zero);
|
||
if (valp)
|
||
__sync_fetch_and_add(valp, 1);
|
||
|
||
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。
|
||
### Eunomia中使用方式
|
||
|
||
|
||
### 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。 |