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

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Message-ID: <20060914222318.GA25004@elte.hu>
Date:	Fri, 15 Sep 2006 00:23:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Michel Dagenais <michel.dagenais@...ymtl.ca>
Cc:	Martin Bligh <mbligh@...igh.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	fche@...hat.com
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108


* Michel Dagenais <michel.dagenais@...ymtl.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
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