Messages in this thread | | | Date | Sat, 16 Jun 2012 02:17:33 -0700 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 02/15] rcu: Size rcu_node tree from nr_cpu_ids rather than NR_CPUS |
| |
On Fri, Jun 15, 2012 at 11:38:48PM -0700, Paul E. McKenney wrote: > On Fri, Jun 15, 2012 at 10:17:12PM -0700, Josh Triplett wrote: > > On Fri, Jun 15, 2012 at 05:37:14PM -0700, Paul E. McKenney wrote: > > > On Fri, Jun 15, 2012 at 02:47:26PM -0700, Josh Triplett wrote: > > > > On Fri, Jun 15, 2012 at 02:05:57PM -0700, Paul E. McKenney wrote: > > > > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > > > > > > > The rcu_node tree array is sized based on compile-time constants, > > > > > including NR_CPUS. Although this approach has worked well in the past, > > > > > the recent trend by many distros to define NR_CPUS=4096 results in > > > > > excessive grace-period-initialization latencies. > > > > > > > > > > This commit therefore substitutes the run-time computed nr_cpu_ids for > > > > > the compile-time NR_CPUS when building the tree. This can result in > > > > > much of the compile-time-allocated rcu_node array being unused. If > > > > > this is a major problem, you are in a specialized situation anyway, > > > > > so you can manually adjust the NR_CPUS, RCU_FANOUT, and RCU_FANOUT_LEAF > > > > > kernel config parameters. > > > > > > > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > > --- > > > > > kernel/rcutree.c | 2 +- > > > > > kernel/rcutree_plugin.h | 2 ++ > > > > > 2 files changed, 3 insertions(+), 1 deletions(-) > > > > > > > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > > > > index a151184..9098910 100644 > > > > > --- a/kernel/rcutree.c > > > > > +++ b/kernel/rcutree.c > > > > > @@ -2672,7 +2672,7 @@ static void __init rcu_init_geometry(void) > > > > > { > > > > > int i; > > > > > int j; > > > > > - int n = NR_CPUS; > > > > > + int n = nr_cpu_ids; > > > > > > > > Same question as before: why have this as a variable when it never > > > > changes? > > > > > > Ah, that explains why. This prevented me from forgetting the random > > > NR_CPUS. > > > > Does that mean it can go away now that you've written the patches? > > If I don't have to change from nr_cpu_ids to yet another thing over > the next while, then it might be worth changing.
That sounds like an argument for a #define or a static const, rather than a local variable. :)
- Josh Triplett
| |