[PATCH net-next 2/2] virtio_net: Stripe queue affinities across cores.

[Caleb Raitto]

From: Caleb Raitto <carai...@google.com>

Always set the affinity hint, even if #cpu != #vq.

Handle the case where #cpu > #vq (including when #cpu % #vq != 0) and
when #vq > #cpu (including when #vq % #cpu != 0).

Signed-off-by: Caleb Raitto <carai...@google.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
Acked-by: Jon Olson <jonol...@google.com>
---
 drivers/net/virtio_net.c | 42 ++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 43fabc0eb4d2..eb00ae6ee475 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -31,6 +31,7 @@
 #include <linux/average.h>
 #include <linux/filter.h>
 #include <linux/netdevice.h>
+#include <linux/kernel.h>
 #include <linux/pci.h>
 #include <net/route.h>
 #include <net/xdp.h>
@@ -1888,30 +1889,41 @@ static void virtnet_clean_affinity(struct virtnet_info 
*vi, long hcpu)
 
 static void virtnet_set_affinity(struct virtnet_info *vi)
 {
-       int i;
-       int cpu;
+       cpumask_var_t mask;
+       int stragglers;
+       int group_size;
+       int i, j, cpu;
+       int num_cpu;
+       int stride;
 
-       /* In multiqueue mode, when the number of cpu is equal to the number of
-        * queue pairs, we let the queue pairs to be private to one cpu by
-        * setting the affinity hint to eliminate the contention.
-        */
-       if (vi->curr_queue_pairs == 1 ||
-           vi->max_queue_pairs != num_online_cpus()) {
+       if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
                virtnet_clean_affinity(vi, -1);
                return;
        }
 
-       i = 0;
-       for_each_online_cpu(cpu) {
-               const unsigned long *mask = cpumask_bits(cpumask_of(cpu));
+       num_cpu = num_online_cpus();
+       stride = max_t(int, num_cpu / vi->curr_queue_pairs, 1);
+       stragglers = num_cpu >= vi->curr_queue_pairs ?
+                       num_cpu % vi->curr_queue_pairs :
+                       0;
+       cpu = cpumask_next(-1, cpu_online_mask);
 
-               virtqueue_set_affinity(vi->rq[i].vq, cpumask_of(cpu));
-               virtqueue_set_affinity(vi->sq[i].vq, cpumask_of(cpu));
-               __netif_set_xps_queue(vi->dev, mask, i, false);
-               i++;
+       for (i = 0; i < vi->curr_queue_pairs; i++) {
+               group_size = stride + (i < stragglers ? 1 : 0);
+
+               for (j = 0; j < group_size; j++) {
+                       cpumask_set_cpu(cpu, mask);
+                       cpu = cpumask_next_wrap(cpu, cpu_online_mask,
+                                               nr_cpu_ids, false);
+               }
+               virtqueue_set_affinity(vi->rq[i].vq, mask);
+               virtqueue_set_affinity(vi->sq[i].vq, mask);
+               __netif_set_xps_queue(vi->dev, cpumask_bits(mask), i, false);
+               cpumask_clear(mask);
        }
 
        vi->affinity_hint_set = true;
+       free_cpumask_var(mask);
 }
 
 static int virtnet_cpu_online(unsigned int cpu, struct hlist_node *node)
-- 
2.18.0.597.ga71716f1ad-goog