kvm_watcher:优化对map数据排序的代码，更新说明文档

eBPF_Supermarket/kvm_watcher/docs/kvm_exit.md

@@ -48,7 +48,7 @@
 ## 示例输出
 
 4391为主机上的虚拟机进程，4508、4509、4510...分别是虚拟机中的vcpu子进程，每隔两秒输出虚拟机中产生的exit事件及其处理延时等信息。
-
+结果会以进程号（VM的唯一标识）以及线程号（VM中每个VCPU的唯一标识）的优先级依次从小到大的顺序输出。
 ```
 ubuntu@rd350x:~/nans/lmp/eBPF_Supermarket/kvm_watcher$ sudo ./kvm_watcher -e
 

eBPF_Supermarket/kvm_watcher/src/kvm_watcher.c

@@ -870,40 +870,27 @@ int sort_by_key(int fd, struct exit_key *keys, struct exit_value *values) {
     struct exit_key lookup_key = {};
     struct exit_key next_key = {};
     struct exit_value exit_value;
-    int first = 1;
-    int i = 0, j;
-    int count = 0;
+    int i = 0, j = 0, count = 0;
     while (!bpf_map_get_next_key(fd, &lookup_key, &next_key)) {
-        count++;
-        if (first) {
-            first = 0;
-            bpf_map_lookup_elem(fd, &next_key, &exit_value);
-            keys[0] = next_key;
-            values[0] = exit_value;
-            i++;
-            lookup_key = next_key;
-            continue;
-        }
+        j = i - 1;
+        struct exit_key temp_key = next_key;
         err = bpf_map_lookup_elem(fd, &next_key, &exit_value);
         if (err < 0) {
             fprintf(stderr, "failed to lookup exit_value: %d\n", err);
             return -1;
         }
-        // insert sort
-        j = i - 1;
-        struct exit_key temp_key = next_key;
         struct exit_value temp_value = exit_value;
         while (j >= 0 &&
                (keys[j].pid > temp_key.pid || (keys[j].tid > temp_key.tid))) {
             keys[j + 1] = keys[j];
             values[j + 1] = values[j];
             j--;
         }
-        i++;
-        keys[j + 1] = next_key;
+        keys[j + 1] = temp_key;
         values[j + 1] = temp_value;
-        // Move to the next key
         lookup_key = next_key;
+        count++;
+        i++;
     }
     return count;
 }