Messages in this thread | | | Date | Fri, 15 Jun 2012 14:47:26 -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 |
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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?
- Josh Triplett
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