[PATCH 1/2] virtio-scsi: split out request queue set affinity function

[Wanlong Gao]

These two patches are based on the multi-queue virtio-scsi patch set.

We set cpu affinity when the num_queues equals to the number
of VCPUs. Split out the set affinity function, this also
fix the bug when CPU IDs are not consecutive.

Signed-off-by: Wanlong Gao <gaowanl...@cn.fujitsu.com>
---
 drivers/scsi/virtio_scsi.c | 50 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 3641d5f..16b0ef2 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -106,6 +106,9 @@ struct virtio_scsi {
 
        u32 num_queues;
 
+       /* Does the affinity hint is set for virtqueues? */
+       bool affinity_hint_set;
+
        struct virtio_scsi_vq ctrl_vq;
        struct virtio_scsi_vq event_vq;
        struct virtio_scsi_vq req_vqs[];
@@ -701,14 +704,45 @@ static struct scsi_host_template 
virtscsi_host_template_multi = {
                                  &__val, sizeof(__val)); \
        })
 
+static void virtscsi_set_affinity(struct virtio_scsi *vscsi, bool affinity)
+{
+       int i;
+       int cpu;
+
+       /* In multiqueue mode, when the number of cpu is equal
+        * to the number of request queues, we let the qeueues
+        * to be private to one cpu by setting the affinity hint
+        * to eliminate the contention.
+        */
+       if ((vscsi->num_queues == 1 ||
+            vscsi->num_queues != num_online_cpus()) && affinity) {
+               if (vscsi->affinity_hint_set)
+                       affinity = false;
+               else
+                       return;
+       }
+
+       if (affinity) {
+               i = 0;
+               for_each_online_cpu(cpu) {
+                       virtqueue_set_affinity(vscsi->req_vqs[i].vq, cpu);
+                       i++;
+               }
+
+               vscsi->affinity_hint_set = true;
+       } else {
+               for (i = 0; i < vscsi->num_queues - VIRTIO_SCSI_VQ_BASE; i++)
+                       virtqueue_set_affinity(vscsi->req_vqs[i].vq, -1);
+
+               vscsi->affinity_hint_set = false;
+       }
+}
 
 static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
-                            struct virtqueue *vq, bool affinity)
+                            struct virtqueue *vq)
 {
        spin_lock_init(&virtscsi_vq->vq_lock);
        virtscsi_vq->vq = vq;
-       if (affinity)
-               virtqueue_set_affinity(vq, vq->index - VIRTIO_SCSI_VQ_BASE);
 }
 
 static void virtscsi_init_tgt(struct virtio_scsi *vscsi, int i)
@@ -736,6 +770,8 @@ static void virtscsi_remove_vqs(struct virtio_device *vdev)
        struct Scsi_Host *sh = virtio_scsi_host(vdev);
        struct virtio_scsi *vscsi = shost_priv(sh);
 
+       virtscsi_set_affinity(vscsi, false);
+
        /* Stop all the virtqueues. */
        vdev->config->reset(vdev);
 
@@ -779,11 +815,13 @@ static int virtscsi_init(struct virtio_device *vdev,
        if (err)
                return err;
 
-       virtscsi_init_vq(&vscsi->ctrl_vq, vqs[0], false);
-       virtscsi_init_vq(&vscsi->event_vq, vqs[1], false);
+       virtscsi_init_vq(&vscsi->ctrl_vq, vqs[0]);
+       virtscsi_init_vq(&vscsi->event_vq, vqs[1]);
        for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++)
                virtscsi_init_vq(&vscsi->req_vqs[i - VIRTIO_SCSI_VQ_BASE],
-                                vqs[i], vscsi->num_queues > 1);
+                                vqs[i]);
+
+       virtscsi_set_affinity(vscsi, true);
 
        virtscsi_config_set(vdev, cdb_size, VIRTIO_SCSI_CDB_SIZE);
        virtscsi_config_set(vdev, sense_size, VIRTIO_SCSI_SENSE_SIZE);
-- 
1.8.1
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