1 files changed, 254 insertions, 28 deletions

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index dc2daec9a10d..8dcdef0783db 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -22,12 +22,14 @@
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 #include <linux/virtio_scsi.h>
+#include <linux/cpu.h>
 #include <scsi/scsi_host.h>
 #include <scsi/scsi_device.h>
 #include <scsi/scsi_cmnd.h>
 
 #define VIRTIO_SCSI_MEMPOOL_SZ 64
 #define VIRTIO_SCSI_EVENT_LEN 8
+#define VIRTIO_SCSI_VQ_BASE 2
 
 /* Command queue element */
 struct virtio_scsi_cmd {
@@ -59,22 +61,58 @@ struct virtio_scsi_vq {
 	struct virtqueue *vq;
 };
 
-/* Per-target queue state */
+/*
+ * Per-target queue state.
+ *
+ * This struct holds the data needed by the queue steering policy.  When a
+ * target is sent multiple requests, we need to drive them to the same queue so
+ * that FIFO processing order is kept.  However, if a target was idle, we can
+ * choose a queue arbitrarily.  In this case the queue is chosen according to
+ * the current VCPU, so the driver expects the number of request queues to be
+ * equal to the number of VCPUs.  This makes it easy and fast to select the
+ * queue, and also lets the driver optimize the IRQ affinity for the virtqueues
+ * (each virtqueue's affinity is set to the CPU that "owns" the queue).
+ *
+ * An interesting effect of this policy is that only writes to req_vq need to
+ * take the tgt_lock.  Read can be done outside the lock because:
+ *
+ * - writes of req_vq only occur when atomic_inc_return(&tgt->reqs) returns 1.
+ *   In that case, no other CPU is reading req_vq: even if they were in
+ *   virtscsi_queuecommand_multi, they would be spinning on tgt_lock.
+ *
+ * - reads of req_vq only occur when the target is not idle (reqs != 0).
+ *   A CPU that enters virtscsi_queuecommand_multi will not modify req_vq.
+ *
+ * Similarly, decrements of reqs are never concurrent with writes of req_vq.
+ * Thus they can happen outside the tgt_lock, provided of course we make reqs
+ * an atomic_t.
+ */
 struct virtio_scsi_target_state {
-	/* Never held at the same time as vq_lock.  */
+	/* This spinlock never held at the same time as vq_lock. */
 	spinlock_t tgt_lock;
+
+	/* Count of outstanding requests. */
+	atomic_t reqs;
+
+	/* Currently active virtqueue for requests sent to this target. */
+	struct virtio_scsi_vq *req_vq;
 };
 
 /* Driver instance state */
 struct virtio_scsi {
 	struct virtio_device *vdev;
 
-	struct virtio_scsi_vq ctrl_vq;
-	struct virtio_scsi_vq event_vq;
-	struct virtio_scsi_vq req_vq;
-
 	/* Get some buffers ready for event vq */
 	struct virtio_scsi_event_node event_list[VIRTIO_SCSI_EVENT_LEN];
+
+	u32 num_queues;
+
+	/* If 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[];
 };
 
 static struct kmem_cache *virtscsi_cmd_cache;
@@ -109,6 +147,8 @@ static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
 	struct virtio_scsi_cmd *cmd = buf;
 	struct scsi_cmnd *sc = cmd->sc;
 	struct virtio_scsi_cmd_resp *resp = &cmd->resp.cmd;
+	struct virtio_scsi_target_state *tgt =
+				scsi_target(sc->device)->hostdata;
 
 	dev_dbg(&sc->device->sdev_gendev,
 		"cmd %p response %u status %#02x sense_len %u\n",
@@ -163,6 +203,8 @@ static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
 
 	mempool_free(cmd, virtscsi_cmd_pool);
 	sc->scsi_done(sc);
+
+	atomic_dec(&tgt->reqs);
 }
 
 static void virtscsi_vq_done(struct virtio_scsi *vscsi,
@@ -187,8 +229,42 @@ static void virtscsi_req_done(struct virtqueue *vq)
 {
 	struct Scsi_Host *sh = virtio_scsi_host(vq->vdev);
 	struct virtio_scsi *vscsi = shost_priv(sh);
+	int index = vq->index - VIRTIO_SCSI_VQ_BASE;
+	struct virtio_scsi_vq *req_vq = &vscsi->req_vqs[index];
 
-	virtscsi_vq_done(vscsi, &vscsi->req_vq, virtscsi_complete_cmd);
+	/*
+	 * Read req_vq before decrementing the reqs field in
+	 * virtscsi_complete_cmd.
+	 *
+	 * With barriers:
+	 *
+	 * 	CPU #0			virtscsi_queuecommand_multi (CPU #1)
+	 * 	------------------------------------------------------------
+	 * 	lock vq_lock
+	 * 	read req_vq
+	 * 	read reqs (reqs = 1)
+	 * 	write reqs (reqs = 0)
+	 * 				increment reqs (reqs = 1)
+	 * 				write req_vq
+	 *
+	 * Possible reordering without barriers:
+	 *
+	 * 	CPU #0			virtscsi_queuecommand_multi (CPU #1)
+	 * 	------------------------------------------------------------
+	 * 	lock vq_lock
+	 * 	read reqs (reqs = 1)
+	 * 	write reqs (reqs = 0)
+	 * 				increment reqs (reqs = 1)
+	 * 				write req_vq
+	 * 	read (wrong) req_vq
+	 *
+	 * We do not need a full smp_rmb, because req_vq is required to get
+	 * to tgt->reqs: tgt is &vscsi->tgt[sc->device->id], where sc is stored
+	 * in the virtqueue as the user token.
+	 */
+	smp_read_barrier_depends();
+
+	virtscsi_vq_done(vscsi, req_vq, virtscsi_complete_cmd);
 };
 
 static void virtscsi_complete_free(struct virtio_scsi *vscsi, void *buf)
@@ -251,7 +327,7 @@ static void virtscsi_cancel_event_work(struct virtio_scsi *vscsi)
 }
 
 static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
-						struct virtio_scsi_event *event)
+					    struct virtio_scsi_event *event)
 {
 	struct scsi_device *sdev;
 	struct Scsi_Host *shost = virtio_scsi_host(vscsi->vdev);
@@ -410,9 +486,10 @@ static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
 	return err;
 }
 
-static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
+static int virtscsi_queuecommand(struct virtio_scsi *vscsi,
+				 struct virtio_scsi_vq *req_vq,
+				 struct scsi_cmnd *sc)
 {
-	struct virtio_scsi *vscsi = shost_priv(sh);
 	struct virtio_scsi_cmd *cmd;
 	int ret;
 
@@ -446,7 +523,7 @@ static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
 	BUG_ON(sc->cmd_len > VIRTIO_SCSI_CDB_SIZE);
 	memcpy(cmd->req.cmd.cdb, sc->cmnd, sc->cmd_len);
 
-	if (virtscsi_kick_cmd(&vscsi->req_vq, cmd,
+	if (virtscsi_kick_cmd(req_vq, cmd,
 			      sizeof cmd->req.cmd, sizeof cmd->resp.cmd,
 			      GFP_ATOMIC) == 0)
 		ret = 0;
@@ -457,6 +534,55 @@ out:
 	return ret;
 }
 
+static int virtscsi_queuecommand_single(struct Scsi_Host *sh,
+					struct scsi_cmnd *sc)
+{
+	struct virtio_scsi *vscsi = shost_priv(sh);
+	struct virtio_scsi_target_state *tgt =
+				scsi_target(sc->device)->hostdata;
+
+	atomic_inc(&tgt->reqs);
+	return virtscsi_queuecommand(vscsi, &vscsi->req_vqs[0], sc);
+}
+
+static struct virtio_scsi_vq *virtscsi_pick_vq(struct virtio_scsi *vscsi,
+					       struct virtio_scsi_target_state *tgt)
+{
+	struct virtio_scsi_vq *vq;
+	unsigned long flags;
+	u32 queue_num;
+
+	spin_lock_irqsave(&tgt->tgt_lock, flags);
+
+	/*
+	 * The memory barrier after atomic_inc_return matches
+	 * the smp_read_barrier_depends() in virtscsi_req_done.
+	 */
+	if (atomic_inc_return(&tgt->reqs) > 1)
+		vq = ACCESS_ONCE(tgt->req_vq);
+	else {
+		queue_num = smp_processor_id();
+		while (unlikely(queue_num >= vscsi->num_queues))
+			queue_num -= vscsi->num_queues;
+
+		tgt->req_vq = vq = &vscsi->req_vqs[queue_num];
+	}
+
+	spin_unlock_irqrestore(&tgt->tgt_lock, flags);
+	return vq;
+}
+
+static int virtscsi_queuecommand_multi(struct Scsi_Host *sh,
+				       struct scsi_cmnd *sc)
+{
+	struct virtio_scsi *vscsi = shost_priv(sh);
+	struct virtio_scsi_target_state *tgt =
+				scsi_target(sc->device)->hostdata;
+	struct virtio_scsi_vq *req_vq = virtscsi_pick_vq(vscsi, tgt);
+
+	return virtscsi_queuecommand(vscsi, req_vq, sc);
+}
+
 static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
 {
 	DECLARE_COMPLETION_ONSTACK(comp);
@@ -533,6 +659,8 @@ static int virtscsi_target_alloc(struct scsi_target *starget)
 		return -ENOMEM;
 
 	spin_lock_init(&tgt->tgt_lock);
+	atomic_set(&tgt->reqs, 0);
+	tgt->req_vq = NULL;
 
 	starget->hostdata = tgt;
 	return 0;
@@ -544,12 +672,28 @@ static void virtscsi_target_destroy(struct scsi_target *starget)
 	kfree(tgt);
 }
 
-static struct scsi_host_template virtscsi_host_template = {
+static struct scsi_host_template virtscsi_host_template_single = {
 	.module = THIS_MODULE,
 	.name = "Virtio SCSI HBA",
 	.proc_name = "virtio_scsi",
-	.queuecommand = virtscsi_queuecommand,
 	.this_id = -1,
+	.queuecommand = virtscsi_queuecommand_single,
+	.eh_abort_handler = virtscsi_abort,
+	.eh_device_reset_handler = virtscsi_device_reset,
+
+	.can_queue = 1024,
+	.dma_boundary = UINT_MAX,
+	.use_clustering = ENABLE_CLUSTERING,
+	.target_alloc = virtscsi_target_alloc,
+	.target_destroy = virtscsi_target_destroy,
+};
+
+static struct scsi_host_template virtscsi_host_template_multi = {
+	.module = THIS_MODULE,
+	.name = "Virtio SCSI HBA",
+	.proc_name = "virtio_scsi",
+	.this_id = -1,
+	.queuecommand = virtscsi_queuecommand_multi,
 	.eh_abort_handler = virtscsi_abort,
 	.eh_device_reset_handler = virtscsi_device_reset,
 
@@ -577,6 +721,47 @@ static struct scsi_host_template virtscsi_host_template = {
 				  &__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_set_affinity(struct virtio_scsi *vscsi, bool affinity)
+{
+	get_online_cpus();
+	__virtscsi_set_affinity(vscsi, affinity);
+	put_online_cpus();
+}
+
 static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
 			     struct virtqueue *vq)
 {
@@ -593,6 +778,11 @@ static void virtscsi_scan(struct virtio_device *vdev)
 
 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);
 
@@ -603,27 +793,43 @@ static int virtscsi_init(struct virtio_device *vdev,
 			 struct virtio_scsi *vscsi)
 {
 	int err;
-	struct virtqueue *vqs[3];
+	u32 i;
+	u32 num_vqs;
+	vq_callback_t **callbacks;
+	const char **names;
+	struct virtqueue **vqs;
+
+	num_vqs = vscsi->num_queues + VIRTIO_SCSI_VQ_BASE;
+	vqs = kmalloc(num_vqs * sizeof(struct virtqueue *), GFP_KERNEL);
+	callbacks = kmalloc(num_vqs * sizeof(vq_callback_t *), GFP_KERNEL);
+	names = kmalloc(num_vqs * sizeof(char *), GFP_KERNEL);
+
+	if (!callbacks || !vqs || !names) {
+		err = -ENOMEM;
+		goto out;
+	}
 
-	vq_callback_t *callbacks[] = {
-		virtscsi_ctrl_done,
-		virtscsi_event_done,
-		virtscsi_req_done
-	};
-	const char *names[] = {
-		"control",
-		"event",
-		"request"
-	};
+	callbacks[0] = virtscsi_ctrl_done;
+	callbacks[1] = virtscsi_event_done;
+	names[0] = "control";
+	names[1] = "event";
+	for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++) {
+		callbacks[i] = virtscsi_req_done;
+		names[i] = "request";
+	}
 
 	/* Discover virtqueues and write information to configuration.  */
-	err = vdev->config->find_vqs(vdev, 3, vqs, callbacks, names);
+	err = vdev->config->find_vqs(vdev, num_vqs, vqs, callbacks, names);
 	if (err)
-		return err;
+		goto out;
 
 	virtscsi_init_vq(&vscsi->ctrl_vq, vqs[0]);
 	virtscsi_init_vq(&vscsi->event_vq, vqs[1]);
-	virtscsi_init_vq(&vscsi->req_vq, vqs[2]);
+	for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++)
+		virtscsi_init_vq(&vscsi->req_vqs[i - VIRTIO_SCSI_VQ_BASE],
+				 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);
@@ -631,6 +837,14 @@ static int virtscsi_init(struct virtio_device *vdev,
 	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
 		virtscsi_kick_event_all(vscsi);
 
+	err = 0;
+
+out:
+	kfree(names);
+	kfree(callbacks);
+	kfree(vqs);
+	if (err)
+		virtscsi_remove_vqs(vdev);
 	return err;
 }
 
@@ -641,10 +855,21 @@ static int virtscsi_probe(struct virtio_device *vdev)
 	int err;
 	u32 sg_elems, num_targets;
 	u32 cmd_per_lun;
+	u32 num_queues;
+	struct scsi_host_template *hostt;
+
+	/* We need to know how many queues before we allocate. */
+	num_queues = virtscsi_config_get(vdev, num_queues) ? : 1;
 
 	num_targets = virtscsi_config_get(vdev, max_target) + 1;
 
-	shost = scsi_host_alloc(&virtscsi_host_template, sizeof(*vscsi));
+	if (num_queues == 1)
+		hostt = &virtscsi_host_template_single;
+	else
+		hostt = &virtscsi_host_template_multi;
+
+	shost = scsi_host_alloc(hostt,
+		sizeof(*vscsi) + sizeof(vscsi->req_vqs[0]) * num_queues);
 	if (!shost)
 		return -ENOMEM;
 
@@ -652,6 +877,7 @@ static int virtscsi_probe(struct virtio_device *vdev)
 	shost->sg_tablesize = sg_elems;
 	vscsi = shost_priv(shost);
 	vscsi->vdev = vdev;
+	vscsi->num_queues = num_queues;
 	vdev->priv = shost;
 
 	err = virtscsi_init(vdev, vscsi);