On Sat, Apr 30, 2011 at 05:59:28AM -0700, Paul E. McKenney wrote: > On Fri, Apr 29, 2011 at 09:02:39PM +0300, Gleb Natapov wrote: > > On Fri, Apr 29, 2011 at 01:39:04AM -0700, Paul E. McKenney wrote: > > > On Fri, Apr 29, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote: > > > > On Thu, Apr 28, 2011 at 12:52:02PM +0300, Gleb Natapov wrote: > > > > > > > > Hmmm.... This is interesting. KVM being a module, we either expand > > > > TINY_RCU's size a bit by making rcu_note_context_switch() be a real > > > > function in rcutiny.c and adding an export, or we expand it by adding > > > > two exports. > > > > > > > > I would like to solve this without making TINY_RCU larger, and preferably > > > > by making it smaller. Any ideas come to mind? (Other than making > > > > KVM depend on CONFIG_SMP, which sounds too much like throwing out the > > > > baby with the bathwater.) > > > > > > Nothing quite like hitting "send" to make an idea show up... > > > > > > In a UP kernel, does it actually help anything to have KVM > > > tell RCU about executing in a guest? If not, could we have a > > > rcu_note_context_switch_kvm() that is a static inline empty function in > > > TINY_RCU and maps to rcu_note_context_switch() for TREE_RCU? > > > > > That will work, but does making rcu_note_context_switch() out of line > > actually increase kernel size? The function is called in two places > > currently, so by making it out of line we make two calling site smaller. > > Will measure it next week. > > One thing to keep in mind... Calling an out-of-line function from > KVM requires an export, each of which significantly increases TINY_RCU's > memory footprint. > > Thanx, Paul > How significantly? As I wrote in other mail I compiled two TINY_RCU kernel with and without the patch and I didn't see memory footprint increase at all. May be I measure it incorrectly, but what I see is that with out of line function + export text section becomes 64 byte bigger, but data section becomes 64 byte smaller: text data bss dec hex filename 4544134 590596 2023424 7158154 6d398a vmlinux inline 4544198 590532 2023424 7158154 6d398a vmlinux.ol out of line -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
