On Sat, Mar 07, 2015 at 06:03:38PM +0100, Alexander Gordeev wrote:
> This update simplifies rcu_init_geometry() code flow
> and makes calculation of the total number of rcu_node
> structures more easy to read.
>
> The update relies on the fact num_rcu_lvl[] is never
> accessed beyond rcu_num_lvls index by the rest of the
> code. Therefore, there is no need initialize the whole
> num_rcu_lvl[].
>
> Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> Signed-off-by: Alexander Gordeev <agord...@redhat.com>
The rest of this series looks promising, but I do have to ask... How have
you tested these? The most straightforward approach would be to find
a KVM-capable system with at least 16 CPUs and type the following from
the top-level directory:
sh tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 34 --duration 5
This will do a series of 16 build-boot-test cycles with various configs
(including various rcu_node tree shapes), and print a summary of the
outcome at the end.
For these sorts of changes, I usually also do some user-level testing.
Thanx, Paul
> ---
> kernel/rcu/tree.c | 24 ++++++++++--------------
> 1 file changed, 10 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index fb89630..f9ef1e0 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3854,7 +3854,6 @@ static void __init rcu_init_geometry(void)
> {
> ulong d;
> int i;
> - int j;
> int rcu_capacity[MAX_RCU_LVLS + 1];
>
> /*
> @@ -3905,24 +3904,21 @@ static void __init rcu_init_geometry(void)
> return;
> }
>
> + /* Calculate the number of levels in the tree. */
> + for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
> + }
> + rcu_num_lvls = i;
> +
> /* Calculate the number of rcu_nodes at each level of the tree. */
> - for (i = 1; i <= MAX_RCU_LVLS; i++)
> - if (nr_cpu_ids <= rcu_capacity[i]) {
> - for (j = 0; j <= i; j++) {
> - int cap = rcu_capacity[i - j];
> - num_rcu_lvl[j] = DIV_ROUND_UP(nr_cpu_ids, cap);
> - }
> - rcu_num_lvls = i;
> - for (j = i + 1; j <= MAX_RCU_LVLS; j++)
> - num_rcu_lvl[j] = 0;
> - break;
> - }
> + for (i = 0; i < rcu_num_lvls; i++) {
> + int cap = rcu_capacity[rcu_num_lvls - i];
> + num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
> + }
>
> /* Calculate the total number of rcu_node structures. */
> rcu_num_nodes = 0;
> - for (i = 0; i <= MAX_RCU_LVLS; i++)
> + for (i = 0; i < rcu_num_lvls; i++)
> rcu_num_nodes += num_rcu_lvl[i];
> - rcu_num_nodes -= nr_cpu_ids;
> }
>
> void __init rcu_init(void)
> --
> 1.8.3.1
>
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