perf_even_open (multiple events together)

[kai_w_]

Hi, I'm new to use PEBS and  perf_event_open. Now, I'm trying to collect two events which are MEM_TRANS_RETIRED:LOAD_LATENCY:ldlat=3  and MEM_UOPS_RETIRED:ALL_STORES. According to http://man7.org/linux/man-pages/man2/perf_event_open.2.html, I use perf_event_open to open first event and I can get a handle,  then I use this haddle as group id to open second event. But after I check result, it seems first event's result is overwrite by second event, I can only get second event's result.  My code is like bellow. Can anyone give me some advice? Thanks.

struct perf_event_attr pe_attr;
   memset(&pe_attr, 0, sizeof(pe_attr));
   pe_attr.size = sizeof(pe_attr);
   pfm_perf_encode_arg_t arg;
   memset(&arg, 0, sizeof(arg));
   arg.size = sizeof(pfm_perf_encode_arg_t);
   arg.attr = &pe_attr;
   char *fstr;
   arg.fstr = &fstr;
   curr_err = pfm_get_os_event_encoding(current_archi->sampling_read_event, PFM_PLM0 | PFM_PLM3, PFM_OS_PERF_EVENT, &arg);
   if (curr_err != PFM_SUCCESS) {
     return ERROR_PFM;
   }
   pe_attr.sample_period = 1000;
   pe_attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR | PERF_SAMPLE_DATA_SRC;  //PERF_SAMPLE_WEIGHT                      
   pe_attr.mmap = 1;
   pe_attr.task = 1;
   pe_attr.precise_ip = 2;

 // Other parameters                                                                                                                             
   pe_attr.disabled = 1;
   pe_attr.exclude_kernel = 1;
   pe_attr.exclude_hv = 1;

    long first_event_tid = perf_event_open(&pe_attr, 0, -1, -1, 0);
    if (first_event_tid == -1) {
      return ERROR_PERF_EVENT_OPEN;
    }

    pe_attr.disabled = 0; // The group leader will start/stop us  
    curr_err = pfm_get_os_event_encoding(current_archi->sampling_write_event, PFM_PLM0 | PFM_PLM3, PFM_OS_PERF_EVENT, &arg);                    
    if (curr_err != PFM_SUCCESS) {                                                                                                              
        return ERROR_PFM;                                                                                                                            
    }
    long second_event_fd = perf_event_open(&pe_attr_w, 0, -1, first_event_tid, 0);                        
    if (second_event_fd == -1) {                                                                                                                   
      return ERROR_PERF_EVENT_OPEN;                                                                                                                
      }  

    ioctl(first_event_tid, PERF_EVENT_IOC_ENABLE, 0);