From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760972AbYFTPj2 (ORCPT ); Fri, 20 Jun 2008 11:39:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760852AbYFTPjJ (ORCPT ); Fri, 20 Jun 2008 11:39:09 -0400 Received: from mx1.redhat.com ([66.187.233.31]:38618 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759716AbYFTPjI (ORCPT ); Fri, 20 Jun 2008 11:39:08 -0400 Date: Fri, 20 Jun 2008 11:38:22 -0400 From: Jason Baron To: Greg KH Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, joe@perches.com, nick@nick-andrew.net, randy.dunlap@oracle.com Subject: Re: [PATCH 2/8] dynamic debug - core infrastructure Message-ID: <20080620153822.GA10639@redhat.com> References: <20080613190039.GC8813@redhat.com> <20080618160812.GB9453@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080618160812.GB9453@kroah.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 18, 2008 at 09:08:12AM -0700, Greg KH wrote: > On Fri, Jun 13, 2008 at 03:00:39PM -0400, Jason Baron wrote: > > --- a/include/linux/device.h > > +++ b/include/linux/device.h > > @@ -595,6 +595,22 @@ extern const char *dev_driver_string(struct device *dev); > > #ifdef DEBUG > > #define dev_dbg(dev, format, arg...) \ > > dev_printk(KERN_DEBUG , dev , format , ## arg) > > +#elif defined(CONFIG_DYNAMIC_PRINTK_DEBUG) > > +#define dev_dbg(dev, format, ...) do { \ > > + static char mod_name[] \ > > + __attribute__((section("__verbose_strings"))) \ > > + = KBUILD_MODNAME; \ > > + static struct mod_debug foobar \ > > + __used \ > > + __attribute__((section("__verbose"), aligned(8))) = \ > > + { mod_name, mod_name, "0", "0", NULL }; \ > > Does the compiler merge all of these variables together into one within > the same file? > no. > If not, should we have a new macro, one per file, for this information? > With this feature enabled, the above 'meta-data' added ~32K to the .init.data section. This memory is freed when the system boots because it is placed in the .init.data section. The same is true for modules, the 'meta-data' is freed when the module loads. We could reduce the vmlinux by having 'register()' type calls for this infrastructure, or a new marco per file as you suggest, and i had something like that in an earlier iteration, but I think the memory savings is very small when compared to the increased complexity. The simplicity to just put a 'pr_debug()" anywhere and just have it do the right thing is nice. Also, it should be noted that the total increase in the size of the 'vmlinux' was 3%, or 2M, this is due to the above 'meta-data', the new code, and probably most significantly, the strings, for the additinal printks. Thus, compressing the above meta-data, or eliminating it by some other means would only decrease the size of this infrastructure by 2% or so. thanks, -Jason