linux-kernel - Re: [PATCH v9] Unified trace buffer

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Date:	Sat, 27 Sep 2008 22:00:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH v9] Unified trace buffer


* Steven Rostedt <rostedt@...dmis.org> wrote:

> >  RINGBUF_TYPE_PADDING
> > 
> > yes, it's longer, but still, saner.
> 
> I don't mind the extra typing, it is just a bit more difficult to keep 
> in the 80 character line limit.

that's really not a hard limit, but yeah.

generally, with clean and simple functions it's easy to keep it.

> > yes, way too big. Sometimes we make savings from a 10 bytes function 
> > already. (but it's always case dependent - if a function has a lot 
> > of parameters then uninlining can hurt)
> > 
> > the only exception would be if there's normally only a single 
> > instantiation per tracer, and if it's in the absolute tracing 
> > hotpath.
> 
> It is a hot path in the internals. Perhaps I'll make an inline 
> function in the interal code "rb_event_length" and have the other 
> users call.
> 
> unsigned ring_buffer_event(struct ring_buffer_event *event)
> {
> 	return rb_event_length(event);
> }

yeah, sounds sane.

> > no, it is not readable. My point was that you should do:
> > > 
> > >    RB_ENUM_TYPE,	/*
> > > 			 * Comment
> > > 			 */
> > > 
> > > The comment is not at the same line as the enum, which also looks 
> > > unpleasing.
> > 
> > but you did:
> > 
> > >    RB_ENUM_TYPE,	/* Comment
> > > 			 */
> > 
> > So i suggested to fix it to:
> > 
> >  +	RB_TYPE_TIME_EXTENT,	/*
> >  +				 * Extent the time delta
> >  +				 * array[0] = time delta (28 .. 59)
> >  +				 * size = 8 bytes
> >  +				 */
> > 
> > ok? I.e. "comment" should have the same visual properties as other 
> > comments.
> > 
> > I fully agree with moving it next to the enum, i sometimes use that 
> > style too, it's a nice touch and more readable in this case than 
> > comment-ahead. (which we use for statements)
> 
> But then we have:
> 
>         RB_TYPE_PADDING,        /*
> 				   * Left over page padding
>                                  * array is ignored
>                                  * size is variable depending on
>                                  * how much padding is needed
>                                  */
>         RB_TYPE_TIME_EXTENT,    /*
> 				   * Extent the time delta
>                                  * array[0] = time delta (28 .. 59)
>                                  * size = 8 bytes
>                                  */
> 
> Where it is not as easy to see which comment is with which enum. 
> Especially when you have many enums. That's why I like the method I 
> used with:

> 
>         RB_TYPE_PADDING,        /* Left over page padding
>                                  * array is ignored
>                                  * size is variable depending on
>                                  * how much padding is needed
>                                  */
>         RB_TYPE_TIME_EXTENT,    /* Extent the time delta
>                                  * array[0] = time delta (28 .. 59)
>                                  * size = 8 bytes
>                                  */
> 
> Where it is very easy to notice which comment goes with which enum.

this:

>         RB_TYPE_PADDING,        /*
> 				   * Left over page padding
>                                  * array is ignored
>                                  * size is variable depending on
>                                  * how much padding is needed
>                                  */
>
>         RB_TYPE_TIME_EXTENT,    /*
> 				   * Extent the time delta
>                                  * array[0] = time delta (28 .. 59)
>                                  * size = 8 bytes
>                                  */

or:

>	/*
>	 * Left over page padding. 'array' is ignored,
>	 * 'size' is variable depending on how much padding is needed.
>	 */
>	RB_TYPE_PADDING,
>
>	/*
>	 * Extent the time delta,
>	 * array[0] = time delta (28 .. 59), size = 8 bytes
>	 */
>	RB_TYPE_TIME_EXTENT,

oh, btw., that's a spelling mistake: s/extend/extend ?

	Ingo
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