Messages in this thread | | | Date | Fri, 20 Jun 2008 11:38:22 -0400 | From | Jason Baron <> | Subject | Re: [PATCH 2/8] dynamic debug - core infrastructure |
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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
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