linux-kernel - Re: [PATCH 0/3] dynamic_debug: Add print_hex_dump

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Message-ID: <20121206021453.GA2834@redhat.com>
Date:	Wed, 5 Dec 2012 21:14:53 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Joe Perches <joe@...ches.com>
Cc:	gregkh@...uxfoundation.org, jim.cromie@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] dynamic_debug: Add print_hex_dump_bytes/debug
 support and cleanups

On Wed, Dec 05, 2012 at 02:05:06PM -0800, Joe Perches wrote:
> On Wed, 2012-12-05 at 16:48 -0500, Jason Baron wrote:
> > Here's a collection of the latest dynamic debug patches that I have
> > pending. 
> 
> Any update on the jump table support?
> 

I have patches that implement the support, although they are a bit hacky
due to header dependencies. However, the main reason I didn't post them
yet is that the 'data' section increases quite a bit due to the
increased table size (text section is reduced, since we are saving
instructions). On x86_64, the the upper 32-bits of each table entry are
always '0xffffffff', so the table could be reduced by a factor of 2.
Although, I haven't figured out a simple way of doing so. Perhaps, the
'data' section bloat is ok, due to the runtime savings, though. I can
dig out the % increase data.

While we're on new features, I think it would be nice to have the ability
to enable the core dynamic debug library - lib/dynamic_debug.c,
independently from the debug statements that use it. So, having
CONFIG_DYNAMIC_DEBUG would just configure the infrastructure bits, and
something such as CONFIG_DYNAMIC_DEBUG_PRINTK could enable pr_debug() and
friends. In that way subsystems that want to use dynamic output can be
enabled/disabled independently. So they could do:

#ifdef CONFIG_DRIVER_FOO_DEBUG
 #define drv_foo_debug() dev_dbg()
#else
 #define drv_foo_debug() {}

where CONFIG_DRIVER_FOO_DEBUG would enable CONFIG_DYNAMIC_DEBUG.

Thanks,

-Jason
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