On Tue, Jan 14, 2014 at 02:42:11PM -0800, David Cohen wrote: > On Fri, Dec 20, 2013 at 12:23:36PM -0800, David Cohen wrote: > > On Fri, Dec 20, 2013 at 08:55:27PM +0100, Pavel Machek wrote: > > > On Sun 2013-12-15 11:25:08, David Cohen wrote: > > > > On Sun, Dec 15, 2013 at 06:51:12PM +0100, Pavel Machek wrote: > > > > > On Thu 2013-12-12 21:18:23, David Cohen wrote: > > > > > > This patch makes SET_SYSTEM_SLEEP_PM_OPS() and SET_RUNTIME_PM_OPS() more > > > > > > smart. > > > > > > > > > > > > Despite those macros check for '#ifdef CONFIG_PM_SLEEP/RUNTIME' to avoid > > > > > > setting the callbacks when such #ifdef's aren't defined, they don't > > > > > > handle compiler to avoid messages like that: > > > > > > > > > > > > drivers/usb/host/xhci-plat.c:200:12: warning: ???xhci_plat_suspend??? defined but not used [-Wunused-function] > > > > > > drivers/usb/host/xhci-plat.c:208:12: warning: ???xhci_plat_resume??? defined but not used [-Wunused-function] > > > > > > > > > > > > As result, those macros get rid of #ifdef's when setting callbacks but > > > > > > not when implementing them. > > > > > > > > > > > > With this patch, drivers using SET_*_PM_OPS() macros don't need to #ifdef > > > > > > the callbacks implementation as well. > > > > > > > > > > Well... Interesting trickery, but it means that resulting kernel > > > > > will be bigge due to the dead functions no? > > > > > > > > Actually, it doesn't get bigger. Before sending the patch I did this > > > > dummy test app: > > > > > > > > -------------------------------------------------------------------------------- > > > > #include <stdio.h> > > > > > > > > #define USE_IT_OR_LOOSE_IT(fn) ((void *)((unsigned long)(fn) - (unsigned long)(fn))) > > > > > > > > #ifdef MAKE_ME_NULL > > > > static int func1(int a) > > > > { > > > > printf("Hey!!\n"); > > > > return 0; > > > > } > > > > #endif > > > > > > I thought that point of this patch series was getting rid of the > > > #ifdefs around the function...? Now I'm confused. > > > > Maybe you're misinterpreting the test :) > > > > This #ifdef is used to make this same test code to replicate both > > scenarios according to -DMAKE_ME_NULL (just pay attention to actual > > resulting code after #ifdef's are tested. the #ifdef here is nor related > > to actual #ifdef on kernel). Here are both scenarios: > > > > (1) Not using my trickery (which needs the function to not be present). > > (2) Using my trickery (which needs to function to stay). > > > > With -DMAKE_ME_NULL we replicate (2), then the function *is* there but > > gcc gets rid of it on resulting binary without warnings if used with -O2. > > > > Without -DMAKE_ME_NULL we replicate (1). The #ifdef will fail and then > > remove the function which is an obvious scenario the function won't be > > part of resulting binary. > > > > If we use -S option to have human readable resulting assembly code > > (which is kind of 1:1 for resulting binary), we can compare the result > > of (1) and (2) and check they are pretty similar. > > This proves gcc behaves as expected with my patch: do not need #ifdef > > and do not generate dead codes to resulting binary. > > > > > > > > > struct global_data { > > > > int (*func)(int); > > > > }; > > > > > > > > static struct global_data gd = { > > > > #ifdef MAKE_ME_NULL > > > > .func = USE_IT_OR_LOOSE_IT(func1), > > > > > > If you have ifdef around the function, why do you need magic here? Why > > > not > > > > This #ifdef is necessary to prevent the function to be used when it > > doesn't exist due to above #ifdef. But once again: don't misinterpret > > the #ifdefs in this test app with the ones in kernel. They are not > > related at all. If it's still confusing you just make 2 test apps > > without #ifdeds out of this one where one keeps the code inside #ifdefs > > and the other doesn't. > > > > > > > > .func = func1 > > > > > > ? > > > > > > Basically the warning tells you that you want the ifdef around the > > > function, too... (Otherwise you waste space). That seems like good > > > warning. > > > > Just check my first explanation. > > Ping :) > > Comments here? I found few problems to be fixed prior to be possible this optimization. Many drivers are calling SET_*_PM_OPS() functions and passing non-defined symbols as argument. It's not triggering compilation issue currently because the drivers synchronize when the symbols are not defined with SET_*_PM_OPS() not using them. But IMHO it's a violation of scopes: all drivers calling SET_*_PM_OPS() should give valid symbols, since it creates an unwanted cross-dependence between those PM functions and their users (why SET_*_PM_OPS() can't use symbols given to them as argument?). I can work on fixing SET_*_PM_OPS() users beforehand in case my proposal here is accepted. Br, David Cohen > > Br, David Cohen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html