On Thu, Apr 12, 2012 at 09:46:16PM +0200, Thomas Gleixner wrote: > On Wed, 11 Apr 2012, John Kacur wrote: > > > Fix build break of the following types. > > > > linux-rt/kernel/rcutree_plugin.h: In function ‘print_cpu_stall_fast_no_hz’: > > linux-rt/kernel/rcutree_plugin.h:2195: error: ‘rcu_idle_gp_timer’ undeclared (first use in this function) > > linux-rt/kernel/rcutree_plugin.h:2195: error: (Each undeclared identifier is reported only once > > linux-rt/kernel/rcutree_plugin.h:2195: error: for each function it appears in.) > > > > The build break only occurs with the PREEMPT_RT_FULL patch applied, however > > the patch is meant to go upstream and be applied to v3.4-rc2 as well because > > it makes the code more legible there, and will reduce the number of places > > where #ifdef PREEMPT_RT_FULL is required should that go upstream someday. OK, I will bite... What is PREEMPT_RT_FULL doing to make rcu_idle_gp_timer, which is under CONFIG_RCU_FAST_NO_HZ, inaccessible to print_cpu_stall_fast_no_hz() which is under both CONFIG_RCU_FAST_NO_HZ and CONFIG_RCU_CPU_STALL_INFO? > -ENOPARSE > > I really have no idea what the patch is solving and which particular > combination of config items is causing the above. > > If you think that the patch should go upstream then please send a > separate one with a changelog which explains the simplifcation. > > I agree that this ifdef maze can do with simplification, but providing > a changelog which tells nothing at all does not make it easier to grok > the problem and understand what's simplified. I must confess that I have been considering re-organizing the #ifdefs in kernel/rcutree_plugin.h so that all variants of a given function are adjacent, but I have not yet felt quite masochistic enough to insert quite that many extra #ifdefs. The current organization is as follows: o Boot-time announce functions. o A large number of plugin functions that have real code for CONFIG_TREE_PREEMPT_RCU and trivial definitions for CONFIG_TREE_RCU. In the 3.3 kernel, this region extends from line 73 to line 1135, and used to be the whole point of this file. This region contains additional #ifdefs for CONFIG_HOTPLUG_CPU, CONFIG_RCU_BOOST (which cannot go into the next region because they are used in this region) CONFIG_RCU_CPU_STALL_VERBOSE, and CONFIG_PROVE_LOCKING. o Another set of plugin functions that have real code for CONFIG_RCU_BOOST and trivial definitions otherwise. In the 3.3 kernel, this region extends from line 1137 to line 1824, and contains additional #ifdefs for CONFIG_HOTPLUG_CPU and CONFIG_RCU_TRACE. o Yet another set of plugin functions that have real code for CONFIG_SMP and trivial definitions otherwise. In the 3.3 kernel this region extends from line 1826 to 1950. This is going away, as CONFIG_TREE_RCU&!CONFIG_SMP will no longer be an option. o The next set of plugin functions have real code for CONFIG_RCU_FAST_NO_HZ and trivial definitions otherwise. In the 3.3 kernel, this region extends from line 1952 to line 2199. This region contains additional #ifdefs for CONFIG_TREE_PREEMPT_RCU. o A new set of plugin functions is going in for CONFIG_RCU_CPU_STALL_INFO. So that is the organization. I might contemplate small changes such as moving a function or two to save a #ifdef, but I would have to be convinced that any wholesale reorganization would actually produce better results. Given the amount of code, don't expect me to be easy to convince. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
