virtio-vdpa: Support interrupt affinity spreading mechanism

To support interrupt affinity spreading mechanism,
this makes use of group_cpus_evenly() to create
an irq callback affinity mask for each virtqueue
of vdpa device. Then we will unify set_vq_affinity
callback to pass the affinity to the vdpa device driver.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Message-Id: <20230323053043.35-4-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/virtio/virtio_vdpa.c

@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/uuid.h>
+#include <linux/group_cpus.h>
 #include <linux/virtio.h>
 #include <linux/vdpa.h>
 #include <linux/virtio_config.h>
@@ -272,6 +273,66 @@ static void virtio_vdpa_del_vqs(struct virtio_device *vdev)
 		virtio_vdpa_del_vq(vq);
 }
 
+static void default_calc_sets(struct irq_affinity *affd, unsigned int affvecs)
+{
+	affd->nr_sets = 1;
+	affd->set_size[0] = affvecs;
+}
+
+static struct cpumask *
+create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
+{
+	unsigned int affvecs = 0, curvec, usedvecs, i;
+	struct cpumask *masks = NULL;
+
+	if (nvecs > affd->pre_vectors + affd->post_vectors)
+		affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
+
+	if (!affd->calc_sets)
+		affd->calc_sets = default_calc_sets;
+
+	affd->calc_sets(affd, affvecs);
+
+	if (!affvecs)
+		return NULL;
+
+	masks = kcalloc(nvecs, sizeof(*masks), GFP_KERNEL);
+	if (!masks)
+		return NULL;
+
+	/* Fill out vectors at the beginning that don't need affinity */
+	for (curvec = 0; curvec < affd->pre_vectors; curvec++)
+		cpumask_setall(&masks[curvec]);
+
+	for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
+		unsigned int this_vecs = affd->set_size[i];
+		int j;
+		struct cpumask *result = group_cpus_evenly(this_vecs);
+
+		if (!result) {
+			kfree(masks);
+			return NULL;
+		}
+
+		for (j = 0; j < this_vecs; j++)
+			cpumask_copy(&masks[curvec + j], &result[j]);
+		kfree(result);
+
+		curvec += this_vecs;
+		usedvecs += this_vecs;
+	}
+
+	/* Fill out vectors at the end that don't need affinity */
+	if (usedvecs >= affvecs)
+		curvec = affd->pre_vectors + affvecs;
+	else
+		curvec = affd->pre_vectors + usedvecs;
+	for (; curvec < nvecs; curvec++)
+		cpumask_setall(&masks[curvec]);
+
+	return masks;
+}
+
 static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 				struct virtqueue *vqs[],
 				vq_callback_t *callbacks[],
@@ -282,9 +343,15 @@ static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 	struct virtio_vdpa_device *vd_dev = to_virtio_vdpa_device(vdev);
 	struct vdpa_device *vdpa = vd_get_vdpa(vdev);
 	const struct vdpa_config_ops *ops = vdpa->config;
+	struct irq_affinity default_affd = { 0 };
+	struct cpumask *masks;
 	struct vdpa_callback cb;
 	int i, err, queue_idx = 0;
 
+	masks = create_affinity_masks(nvqs, desc ? desc : &default_affd);
+	if (!masks)
+		return -ENOMEM;
+
 	for (i = 0; i < nvqs; ++i) {
 		if (!names[i]) {
 			vqs[i] = NULL;
@@ -298,6 +365,7 @@ static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 			err = PTR_ERR(vqs[i]);
 			goto err_setup_vq;
 		}
+		ops->set_vq_affinity(vdpa, i, &masks[i]);
 	}
 
 	cb.callback = virtio_vdpa_config_cb;