linux-kernel - Re: [PATCH 18/20] ceph: debugging

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Date:	Fri, 17 Jul 2009 14:35:16 -0700 (PDT)
From:	Sage Weil <sage@...dream.net>
To:	Andi Kleen <andi@...stfloor.org>
cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 18/20] ceph: debugging

On Fri, 17 Jul 2009, Andi Kleen wrote:
> On Fri, Jul 17, 2009 at 12:52:33PM -0700, Sage Weil wrote:
> > > > 		 ceph_file_part(__FILE__, sizeof(__FILE__)),		\
> > > > 		 __LINE__, args);
> > > 
> > > That seems like a wasteful way to do this -- i bet you could
> > > shrink binary size with debugging on considerably if you move
> > > the file_part into a function.
> > 
> > If you mean ceph_file_part shouldn't be inline, definitely.  Beyond that 
> > I'm not sure what more to change... it's just a few extra chars on the 
> > format string and 2 calls instead of 1?
> 
> Yes, but you have hundreds/thousands of these calls don't you?
> 
> If you have two calls here instead of one and that costs let's say
> 20 bytes of code and 1000 calls it's already 20K of binary size.
> 
> Perhaps code size is not your highest priority now, but 
> obvious inefficiencies like this are not good.

Is that really a concern when compiling with DEBUG or 
CONFIG_DYNAMIC_DEBUG?  Since pr_debug is a no-op without those anyway, how 
about:

---

#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
extern const char *ceph_file_part(const char *s, int len);
# define dout(fmt, ...)							\
	pr_debug(" %12.12s:%-4d : " fmt,				\
		 ceph_file_part(__FILE__, sizeof(__FILE__)),		\
		 __LINE__, ##__VA_ARGS__);
#else
/*
 * this is a no-op, but keep the faux printk call just so we see any
 * compiler warnings.
 */
# define dout(fmt, ...)	do {						\
		if (0) printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__);	\
	} while (0)
#endif
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