Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

[Ingo Molnar <mingo@elte.hu>]

* Michel Dagenais <michel.dagenais@polymtl.ca> wrote:

> > the question is: what is more maintainance, hundreds of static 
> > tracepoints (with long parameter lists) all around the (core) kernel, or 
> > hundreds of detached dynamic rules that need an update every now and 
> > then? [but of which most would still be usable even if some of them 
> > "broke"] To me the answer is clear: having hundreds of tracepoints 
> > _within_ the source code is higher cost. But please prove me wrong :-)
> 
> Actually I rarely find that any of the 70 000 printk is such a huge 
> nuisance to code readability. They may even help understand what is 
> going on in a code area you are less familiar with.

i disagree. Consider the following example from LTT:

 int sock_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 {
         struct kiocb iocb;
         struct sock_iocb siocb;
         int ret;

         trace_socket_sendmsg(sock, sock->sk->sk_family,
                 sock->sk->sk_type,
                 sock->sk->sk_protocol,
                 size);

         init_sync_kiocb(&iocb, NULL);
         iocb.private = &siocb;
         ret = __sock_sendmsg(&iocb, sock, msg, size);
         if (-EIOCBQUEUED == ret)
                 ret = wait_on_sync_kiocb(&iocb);
         return ret;
 }

what do the 5 extra lines introduced by trace_socket_sendmsg() tell us? 
Nothing. They mostly just duplicate the information i already have from 
the function declaration. They obscure the clear view of the function:

 int sock_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 {
         struct kiocb iocb;
         struct sock_iocb siocb;
         int ret;

         init_sync_kiocb(&iocb, NULL);
         iocb.private = &siocb;
         ret = __sock_sendmsg(&iocb, sock, msg, size);
         if (-EIOCBQUEUED == ret)
                 ret = wait_on_sync_kiocb(&iocb);
         return ret;
 }

the resulting visual and structural redundancy hurts.

	Ingo