[PATCH] genirq/affinity: report extra vectors on uneven nodes

[Jon Derrick]

The current irq spreading algorithm spreads vectors amongst cpus evenly
per node. If a node has more cpus than another node, the extra vectors
being spread may not be reported back to the caller.

This is most apparent with the NVMe driver and nr_cpus < vectors, where
the underreporting results in the caller's WARN being triggered:

irq_build_affinity_masks()
...
        if (nr_present < numvecs)
                WARN_ON(nr_present + nr_others < numvecs);

Signed-off-by: Jon Derrick <jonathan.derr...@intel.com>
---
 kernel/irq/affinity.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 4352b08ae48d..9beafb8c7e92 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -127,7 +127,8 @@ static int __irq_build_affinity_masks(unsigned int startvec,
        }
 
        for_each_node_mask(n, nodemsk) {
-               unsigned int ncpus, v, vecs_to_assign, vecs_per_node;
+               unsigned int ncpus, v, vecs_to_assign, total_vecs_to_assign,
+                       vecs_per_node;
 
                /* Spread the vectors per node */
                vecs_per_node = (numvecs - (curvec - firstvec)) / nodes;
@@ -141,14 +142,16 @@ static int __irq_build_affinity_masks(unsigned int 
startvec,
 
                /* Account for rounding errors */
                extra_vecs = ncpus - vecs_to_assign * (ncpus / vecs_to_assign);
+               total_vecs_to_assign = vecs_to_assign + extra_vecs;
 
-               for (v = 0; curvec < last_affv && v < vecs_to_assign;
+               for (v = 0; curvec < last_affv && v < total_vecs_to_assign;
                     curvec++, v++) {
                        cpus_per_vec = ncpus / vecs_to_assign;
 
                        /* Account for extra vectors to compensate rounding 
errors */
                        if (extra_vecs) {
                                cpus_per_vec++;
+                               v++;
                                --extra_vecs;
                        }
                        irq_spread_init_one(&masks[curvec].mask, nmsk,
-- 
2.20.1