tcm_vhost: Multi-queue support

This adds virtio-scsi multi-queue support to tcm_vhost. In order to use
multi-queue, guest side multi-queue support is need. It can
be found here:

   https://lkml.org/lkml/2012/12/18/166

Currently, only one thread is created by vhost core code for each
vhost_scsi instance. Even if there are multi-queues, all the handling of
guest kick (vhost_scsi_handle_kick) are processed in one thread. This is
not optimal. Luckily, most of the work is offloaded to the tcm_vhost
workqueue.

Some initial perf numbers:
1 queue,  4 targets, 1 lun per target
4K request size, 50% randread + 50% randwrite: 127K/127k IOPS

4 queues, 4 targets, 1 lun per target
4K request size, 50% randread + 50% randwrite: 181K/181k IOPS

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

2 files changed, 31 insertions, 17 deletions

diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 81ecda54b923..9951297b2427 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -48,6 +48,7 @@
 #include <linux/virtio_net.h> /* TODO vhost.h currently depends on this */
 #include <linux/virtio_scsi.h>
 #include <linux/llist.h>
+#include <linux/bitmap.h>
 
 #include "vhost.c"
 #include "vhost.h"
@@ -59,7 +60,8 @@ enum {
         VHOST_SCSI_VQ_IO = 2,
 };
 
-#define VHOST_SCSI_MAX_TARGET 256
+#define VHOST_SCSI_MAX_TARGET   256
+#define VHOST_SCSI_MAX_VQ       128
 
 struct vhost_scsi {
         /* Protected by vhost_scsi->dev.mutex */
@@ -68,7 +70,7 @@ struct vhost_scsi {
         bool vs_endpoint;
 
         struct vhost_dev dev;
-        struct vhost_virtqueue vqs[3];
+        struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ];
 
         struct vhost_work vs_completion_work; /* cmd completion work item */
         struct llist_head vs_completion_list; /* cmd completion queue */
@@ -366,12 +368,14 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 {
         struct vhost_scsi *vs = container_of(work, struct vhost_scsi,
                                         vs_completion_work);
+        DECLARE_BITMAP(signal, VHOST_SCSI_MAX_VQ);
         struct virtio_scsi_cmd_resp v_rsp;
         struct tcm_vhost_cmd *tv_cmd;
         struct llist_node *llnode;
         struct se_cmd *se_cmd;
-        int ret;
+        int ret, vq;
 
+        bitmap_zero(signal, VHOST_SCSI_MAX_VQ);
         llnode = llist_del_all(&vs->vs_completion_list);
         while (llnode) {
                 tv_cmd = llist_entry(llnode, struct tcm_vhost_cmd,
@@ -390,15 +394,20 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
                 memcpy(v_rsp.sense, tv_cmd->tvc_sense_buf,
                        v_rsp.sense_len);
                 ret = copy_to_user(tv_cmd->tvc_resp, &v_rsp, sizeof(v_rsp));
-                if (likely(ret == 0))
-                        vhost_add_used(&vs->vqs[2], tv_cmd->tvc_vq_desc, 0);
-                else
+                if (likely(ret == 0)) {
+                        vhost_add_used(tv_cmd->tvc_vq, tv_cmd->tvc_vq_desc, 0);
+                        vq = tv_cmd->tvc_vq - vs->vqs;
+                        __set_bit(vq, signal);
+                } else
                         pr_err("Faulted on virtio_scsi_cmd_resp\n");
 
                 vhost_scsi_free_cmd(tv_cmd);
         }
 
-        vhost_signal(&vs->dev, &vs->vqs[2]);
+        vq = -1;
+        while ((vq = find_next_bit(signal, VHOST_SCSI_MAX_VQ, vq + 1))
+                < VHOST_SCSI_MAX_VQ)
+                vhost_signal(&vs->dev, &vs->vqs[vq]);
 }
 
 static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
@@ -561,9 +570,9 @@ static void tcm_vhost_submission_work(struct work_struct *work)
         }
 }
 
-static void vhost_scsi_handle_vq(struct vhost_scsi *vs)
+static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
+        struct vhost_virtqueue *vq)
 {
-        struct vhost_virtqueue *vq = &vs->vqs[2];
         struct virtio_scsi_cmd_req v_req;
         struct tcm_vhost_tpg *tv_tpg;
         struct tcm_vhost_cmd *tv_cmd;
@@ -656,7 +665,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs)
                         ret = __copy_to_user(resp, &rsp, sizeof(rsp));
                         if (!ret)
                                 vhost_add_used_and_signal(&vs->dev,
-                                                &vs->vqs[2], head, 0);
+                                                          vq, head, 0);
                         else
                                 pr_err("Faulted on virtio_scsi_cmd_resp\n");
 
@@ -678,6 +687,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs)
                         ": %d\n", tv_cmd, exp_data_len, data_direction);
 
                 tv_cmd->tvc_vhost = vs;
+                tv_cmd->tvc_vq = vq;
 
                 if (unlikely(vq->iov[out].iov_len !=
                                 sizeof(struct virtio_scsi_cmd_resp))) {
@@ -758,7 +768,7 @@ static void vhost_scsi_handle_kick(struct vhost_work *work)
                                                 poll.work);
         struct vhost_scsi *vs = container_of(vq->dev, struct vhost_scsi, dev);
 
-        vhost_scsi_handle_vq(vs);
+        vhost_scsi_handle_vq(vs, vq);
 }
 
 /*
@@ -879,7 +889,7 @@ err:
 static int vhost_scsi_open(struct inode *inode, struct file *f)
 {
         struct vhost_scsi *s;
-        int r;
+        int r, i;
 
         s = kzalloc(sizeof(*s), GFP_KERNEL);
         if (!s)
@@ -889,8 +899,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
 
         s->vqs[VHOST_SCSI_VQ_CTL].handle_kick = vhost_scsi_ctl_handle_kick;
         s->vqs[VHOST_SCSI_VQ_EVT].handle_kick = vhost_scsi_evt_handle_kick;
-        s->vqs[VHOST_SCSI_VQ_IO].handle_kick = vhost_scsi_handle_kick;
-        r = vhost_dev_init(&s->dev, s->vqs, 3);
+        for (i = VHOST_SCSI_VQ_IO; i < VHOST_SCSI_MAX_VQ; i++)
+                s->vqs[i].handle_kick = vhost_scsi_handle_kick;
+        r = vhost_dev_init(&s->dev, s->vqs, VHOST_SCSI_MAX_VQ);
         if (r < 0) {
                 kfree(s);
                 return r;
@@ -922,9 +933,10 @@ static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
 
 static void vhost_scsi_flush(struct vhost_scsi *vs)
 {
-        vhost_scsi_flush_vq(vs, VHOST_SCSI_VQ_CTL);
-        vhost_scsi_flush_vq(vs, VHOST_SCSI_VQ_EVT);
-        vhost_scsi_flush_vq(vs, VHOST_SCSI_VQ_IO);
+        int i;
+
+        for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
+                vhost_scsi_flush_vq(vs, i);
 }
 
 static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
index 519a5504d347..1d2ae7a60e11 100644
--- a/drivers/vhost/tcm_vhost.h
+++ b/drivers/vhost/tcm_vhost.h
@@ -23,6 +23,8 @@ struct tcm_vhost_cmd {
         struct virtio_scsi_cmd_resp __user *tvc_resp;
         /* Pointer to vhost_scsi for our device */
         struct vhost_scsi *tvc_vhost;
+        /* Pointer to vhost_virtqueue for the cmd */
+        struct vhost_virtqueue *tvc_vq;
         /* Pointer to vhost nexus memory */
         struct tcm_vhost_nexus *tvc_nexus;
         /* The TCM I/O descriptor that is accessed via container_of() */