On Mon, Mar 09, 2015 at 02:35:42PM -0700, Paul E. McKenney wrote: > On Mon, Mar 09, 2015 at 09:36:52AM +0000, Alexander Gordeev wrote: > > On Mon, Mar 09, 2015 at 09:34:04AM +0100, Alexander Gordeev wrote: > > > Hi Paul, > > > > > > Here is cleanup of RCU tree initialization rebased on linux-rcu rcu/next > > > repo, as you requested. Please, note an extra patch #10 that was not > > > present in the first post. > > > > Paul, > > > > Please, ignore patch #10 for now. I missed to notice rcu_node::grpnum is > > used in tracing, so the patch is incomplete. I am not sure why trailing > > spaces in seq_printf(m, "%lx/%lx->%lx %c%c>%c %d:%d ^%d ", ....) are > > needed for, so not sure if "^%d" part should be removed (possibly with > > the traling spaces) or replaced with three spaces. > > OK, dropping this one for the moment. > > The original use of ->grpnum was for manual debugging purposes. Yes, you > can get the same information out of ->grpmask, but the number is easier > to read. And on the debugfs trace information, ->grpnum is printed, > but ->grpmask is not. > > The trailing spaces on the seq_printf() allow the rcu_node data to be > printed on a single line, while still allowing the eye to pick out > where one rcu_node structure's data ends and the next one begins. > > So here are the choices, as far as I can see: > > 1. Leave ->grpnum as is. > > 2. Remove ->grpnum, but regenerate it in print_one_rcu_state(), > for example, by counting the number of rcu_node structures > since the last ->level change. > > 3. Drop ->grpnum and also remove it from the debugfs tracing. > The reader can rely on the ->grplo and ->grphi fields to > work out where this rcu_node structure fits in, but we > lose the visual indication of any bugs in computing these > quantities. > > 4. Drop ->grpnum and replace it with ->grpmask. This seems a > bit obtuse to me. > > 5. Redesign print_one_rcu_state()'s output from scratch. > > #1 has certain advantages from a laziness viewpoint. #2 would open up > some space in the rcu_node structure, but space really isn't an issue > for that structure given that huge systems have only 257 of them and > the really small systems use Tiny RCU instead. #3 might be OK, but I > am not really convinced. #4 seems a bit ugly. I am not signing up > for #5, in part because not all that many people use RCU's debugfs > output, so I don't see the point in investing the time. > > But what did you have in mind?
I probably should have marked this patch as an RFC. Given your summary #1 seems as the best choice. However, I have something else in mind, indeed. What is the reason to have 'grpnum' and 'level' as u8 while, say 'grplo' and 'grphi' - as int? IOW, do we conserve on memory for this structure or not? Thanks! > Thanx, Paul > -- Regards, Alexander Gordeev [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
