The most common case for certain node_random usage (demotion nodemask) is with
nodemask weight 1. We can avoid calling get_random_init() in that case and
always return the only node set in the nodemask.
A simple test as below
before = rdtsc_ordered();
for (i= 0; i < 100; i++) {
rand = node_random(&nmask);
}
after = rdtsc_ordered();
Without fix after - before : 16438
With fix after - before : 816
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
include/linux/nodemask.h | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index 4b71a96190a8..ac5b6a371be5 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -504,12 +504,21 @@ static inline int num_node_state(enum node_states state)
static inline int node_random(const nodemask_t *maskp)
{
#if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1)
- int w, bit = NUMA_NO_NODE;
+ int w, bit;
w = nodes_weight(*maskp);
- if (w)
+ switch (w) {
+ case 0:
+ bit = NUMA_NO_NODE;
+ break;
+ case 1:
+ bit = first_node(*maskp);
+ break;
+ default:
bit = bitmap_ord_to_pos(maskp->bits,
- get_random_int() % w, MAX_NUMNODES);
+ get_random_int() % w, MAX_NUMNODES);
+ break;
+ }
return bit;
#else
return 0;
--
2.37.2
