Re: how to register an event handler for the instance

[christopher lee <christopher.lee.eu@gmail.com>]

Hi Steven, 

>On Mon, 2022-05-16 at 14:14 -0400, Steven Rostedt wrote:
> 
> 
> Are you only looking to reading some events or all of them?

I created several instances and only enabled one trace event in each
instance. I need to read all trace data from each trace_pipe in each
instance and parse the trace information in each instance's associated
thread. I found that if I read tace_pipe, then parse string, it will
not consume so much CPU resource.

> 
> > this file, the handler would not be able to get trace information.
> > Becuase if I read this file, and also call tep_print_event() will
> > consume lots of CPU resoruce. how can I parse the trace event info
> > without reading this file?
> 
> The tep_print_event() is easier to use, but you can do things
> manually as
> well. I'll need to write a tutorial to explain this more, but I can
> help
> you here.
> 

Thanks so much for your support!!

> >  
> > 
> >         for (i = 0; ; i++)
> > {                                          
> >                 char
> > *raw_buf;                                        
> >                 char
> > *cpu;                                            
> >                                                                    
> >                                  
> >                 ret = asprintf(&cpu, "%s/cpu%d", per_cpu,
> > i);         
> >                 if (ret <
> > 0)                                          
> >                         pdie("Could not allocate memory for cpu
> > buffer
> > %d name", i);                
> >                                                                    
> >                                  
> >                 ret = stat(cpu,
> > &st);                                 
> >                 if (ret < 0 || !S_ISDIR(st.st_mode))
> > {                
> >                        
> > free(cpu);                                    
> >                         goto
> > start;                                   
> >                
> > }                                                     
> >                                                                    
> >                                  
> >                 ret = asprintf(&raw_buf, "%s/trace_pipe_raw",
> > cpu);   
> >                 if (ret <
> > 0)                                          
> >                         pdie("Could not allocate memory for cpu %d
> > raw
> > buffer name", i);            
> >                                                                    
> >                                  
> >                 read_raw_buffer(i,
> > raw_buf);                          
> 
> This your own code?
> 

no, it is your code, from your example.


> There is a way to read it yourself and to pick and choose the evens
> you
> want.
> 
> If you read the raw data, you'll need to read it in page size (found
> in the
> header tep file) tep_get_page_size(). And read one page at a time.
> Then you
> can use the kbuffer code (although I haven't finished the man pages
> for
> them)
> 
> Look at the traceevent/kbuffer.h file supplied by libtraceevent.
> 
> You can do something like the following:
> 
>         unsigned long long ts; // time stamp of event
>         struct tep_record record; // should probably be allocated
> 
>         /* For little endian 64 bit machines */
>         kbuf = kbuffer_alloc(KBUFFER_LSIZE_8, KBUFFER_ENDIAN_LITTLE);
> 
>         read(fd, buf, page_size);
> 
>         kbuffer_load_subbuffer(kbuf, buf);
> 
>         data = kbuffer_read_event(kbuf, &ts);
> 
>         if (!data)
>                 return; // end of sub buffer.
> 
>         /* Move the kbuf cursor to the next event */
>         kbuffer_next_event(kbuf, NULL);
> 
>         /* Now data has the record */
> 
>         record.ts = ts;
>         record.size = kbuffer_event_size(kbuf);
>         record.cpu = cpu; // CPU of the trace_pipe_raw file
>         record.data = data;
>         record.missed_events = kbuffer_missed_events(kbuf);
> 

Got it now, I should measure its CPU usage and get back to you here.

Kind regards,
Christ.
> >