Add an alternate I/O path that implements ->make_request for virtio-blk.
This is required for high IOPs devices which get slowed down to 1/5th of
the native speed by all the locking, memory allocation and other overhead
in the request based I/O path.
This patch is not quite merge ready due to two issues:
- it doesn't implement FUA and FLUSH requests yet
- it hardcodes which I/O path to chose
Signed-off-by: Christoph Hellwig <h...@lst.de>
Index: linux-2.6/drivers/block/virtio_blk.c
===================================================================
--- linux-2.6.orig/drivers/block/virtio_blk.c 2011-10-05 10:36:42.883913334
-0400
+++ linux-2.6/drivers/block/virtio_blk.c 2011-10-05 15:29:35.591405323
-0400
@@ -11,6 +11,8 @@
#define PART_BITS 4
+static int use_make_request = 1;
+
static int major, index;
struct workqueue_struct *virtblk_wq;
@@ -20,6 +22,7 @@ struct virtio_blk
struct virtio_device *vdev;
struct virtqueue *vq;
+ wait_queue_head_t queue_wait;
/* The disk structure for the kernel. */
struct gendisk *disk;
@@ -39,11 +42,13 @@ struct virtio_blk
struct virtblk_req
{
void *private;
+ struct virtblk_req *next;
struct virtio_blk_outhdr out_hdr;
struct virtio_scsi_inhdr in_hdr;
u8 kind;
#define VIRTIO_BLK_REQUEST 0x00
-#define VIRTIO_BLK_INTERNAL 0x01
+#define VIRTIO_BLK_BIO 0x01
+#define VIRTIO_BLK_INTERNAL 0x02
u8 status;
};
@@ -74,10 +79,17 @@ static void virtblk_request_done(struct
mempool_free(vbr, vblk->pool);
}
+static void virtblk_bio_done(struct virtio_blk *vblk,
+ struct virtblk_req *vbr)
+{
+ bio_endio(vbr->private, virtblk_result(vbr));
+ mempool_free(vbr, vblk->pool);
+}
+
static void blk_done(struct virtqueue *vq)
{
struct virtio_blk *vblk = vq->vdev->priv;
- struct virtblk_req *vbr;
+ struct virtblk_req *vbr, *head = NULL, *tail = NULL;
unsigned int len;
unsigned long flags;
@@ -88,15 +100,47 @@ static void blk_done(struct virtqueue *v
virtblk_request_done(vblk, vbr);
break;
case VIRTIO_BLK_INTERNAL:
- complete(vbr->private);
+ case VIRTIO_BLK_BIO:
+ if (head) {
+ tail->next = vbr;
+ tail = vbr;
+ } else {
+ tail = head = vbr;
+ }
break;
default:
BUG();
}
}
- /* In case queue is stopped waiting for more buffers. */
- blk_start_queue(vblk->disk->queue);
+
+ if (!use_make_request) {
+ /* In case queue is stopped waiting for more buffers. */
+ blk_start_queue(vblk->disk->queue);
+ }
spin_unlock_irqrestore(&vblk->lock, flags);
+
+ wake_up(&vblk->queue_wait);
+
+ /*
+ * Process completions after freeing up space in the virtqueue and
+ * dropping the lock.
+ */
+ while (head) {
+ vbr = head;
+ head = head->next;
+
+ switch (vbr->kind) {
+ case VIRTIO_BLK_BIO:
+ virtblk_bio_done(vblk, vbr);
+ break;
+ case VIRTIO_BLK_INTERNAL:
+ complete(vbr->private);
+ break;
+ default:
+ BUG();
+ }
+
+ }
}
static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
@@ -111,6 +155,7 @@ static bool do_req(struct request_queue
return false;
vbr->private = req;
+ vbr->next = NULL;
vbr->kind = VIRTIO_BLK_REQUEST;
if (req->cmd_flags & REQ_FLUSH) {
@@ -199,6 +244,128 @@ static void do_virtblk_request(struct re
virtqueue_kick(vblk->vq);
}
+struct virtblk_plug_cb {
+ struct blk_plug_cb cb;
+ struct virtio_blk *vblk;
+};
+
+static void virtblk_unplug(struct blk_plug_cb *bcb)
+{
+ struct virtblk_plug_cb *cb =
+ container_of(bcb, struct virtblk_plug_cb, cb);
+
+ virtqueue_notify(cb->vblk->vq);
+ kfree(cb);
+}
+
+static bool virtblk_plugged(struct virtio_blk *vblk)
+{
+ struct blk_plug *plug = current->plug;
+ struct virtblk_plug_cb *cb;
+
+ if (!plug)
+ return false;
+
+ list_for_each_entry(cb, &plug->cb_list, cb.list) {
+ if (cb->cb.callback == virtblk_unplug && cb->vblk == vblk)
+ return true;
+ }
+
+ /* Not currently on the callback list */
+ cb = kmalloc(sizeof(*cb), GFP_ATOMIC);
+ if (!cb)
+ return false;
+
+ cb->vblk = vblk;
+ cb->cb.callback = virtblk_unplug;
+ list_add(&cb->cb.list, &plug->cb_list);
+ return true;
+}
+
+static void virtblk_add_buf_wait(struct virtio_blk *vblk,
+ struct virtblk_req *vbr, unsigned long out, unsigned long in)
+{
+ DEFINE_WAIT(wait);
+ bool retry, notify;
+
+ for (;;) {
+ prepare_to_wait(&vblk->queue_wait, &wait,
+ TASK_UNINTERRUPTIBLE);
+
+ spin_lock_irq(&vblk->lock);
+ if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr) < 0) {
+ retry = true;
+ } else {
+ retry = false;
+ }
+ notify = virtqueue_kick_prepare(vblk->vq);
+ spin_unlock_irq(&vblk->lock);
+
+ if (notify)
+ virtqueue_notify(vblk->vq);
+
+ if (!retry)
+ break;
+ schedule();
+ }
+ finish_wait(&vblk->queue_wait, &wait);
+}
+
+static int virtblk_make_request(struct request_queue *q, struct bio *bio)
+{
+ struct virtio_blk *vblk = q->queuedata;
+ unsigned long num, out = 0, in = 0;
+ struct virtblk_req *vbr;
+ bool retry, notify;
+
+ BUG_ON(bio->bi_phys_segments + 2 > vblk->sg_elems);
+ BUG_ON(bio->bi_rw & (REQ_FLUSH | REQ_FUA));
+
+ vbr = mempool_alloc(vblk->pool, GFP_NOIO);
+
+ vbr->private = bio;
+ vbr->next = NULL;
+ vbr->kind = VIRTIO_BLK_BIO;
+
+ vbr->out_hdr.type = 0;
+ vbr->out_hdr.sector = bio->bi_sector;
+ vbr->out_hdr.ioprio = bio_prio(bio);
+
+ sg_set_buf(&vblk->sg[out++], &vbr->out_hdr, sizeof(vbr->out_hdr));
+
+ num = bio_map_sg(q, bio, vblk->sg + out);
+
+ sg_set_buf(&vblk->sg[num + out + in++], &vbr->status,
+ sizeof(vbr->status));
+
+ if (num) {
+ if (bio->bi_rw & REQ_WRITE) {
+ vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
+ out += num;
+ } else {
+ vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
+ in += num;
+ }
+ }
+
+ spin_lock_irq(&vblk->lock);
+ if (virtqueue_add_buf(vblk->vq, vblk->sg, out, in, vbr) < 0) {
+ retry = true;
+ } else {
+ retry = false;
+ }
+
+ notify = virtqueue_kick_prepare(vblk->vq);
+ spin_unlock_irq(&vblk->lock);
+
+ if (notify && !virtblk_plugged(vblk))
+ virtqueue_notify(vblk->vq);
+
+ if (retry)
+ virtblk_add_buf_wait(vblk, vbr, out, in);
+ return 0;
+}
+
/* return id (s/n) string for *disk to *id_str
*/
static int virtblk_get_id(struct gendisk *disk, char *id_str)
@@ -212,6 +379,7 @@ static int virtblk_get_id(struct gendisk
if (!vbr)
return -ENOMEM;
vbr->private = &done;
+ vbr->next = NULL;
vbr->kind = VIRTIO_BLK_INTERNAL;
vbr->out_hdr.type = VIRTIO_BLK_T_GET_ID | VIRTIO_BLK_T_IN;
@@ -248,7 +416,8 @@ static int virtblk_ioctl(struct block_de
/*
* Only allow the generic SCSI ioctls if the host can support it.
*/
- if (!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_SCSI))
+ if (!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_SCSI) &&
+ !use_make_request)
return -ENOTTY;
return scsi_cmd_ioctl(disk->queue, disk, mode, cmd,
@@ -383,6 +552,7 @@ static int __devinit virtblk_probe(struc
goto out;
}
+ init_waitqueue_head(&vblk->queue_wait);
spin_lock_init(&vblk->lock);
vblk->vdev = vdev;
vblk->sg_elems = sg_elems;
@@ -409,10 +579,20 @@ static int __devinit virtblk_probe(struc
goto out_mempool;
}
- q = vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
- if (!q) {
- err = -ENOMEM;
- goto out_put_disk;
+ if (use_make_request) {
+ q = vblk->disk->queue = blk_alloc_queue(GFP_KERNEL);
+ if (!q) {
+ err = -ENOMEM;
+ goto out_put_disk;
+ }
+ blk_queue_make_request(q, virtblk_make_request);
+ printk("virtio-blk: using bios directly\n");
+ } else {
+ q = vblk->disk->queue = blk_init_queue(do_virtblk_request,
&vblk->lock);
+ if (!q) {
+ err = -ENOMEM;
+ goto out_put_disk;
+ }
}
q->queuedata = vblk;
@@ -438,7 +618,7 @@ static int __devinit virtblk_probe(struc
index++;
/* configure queue flush support */
- if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+ if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH) && !use_make_request)
blk_queue_flush(q, REQ_FLUSH);
/* If disk is read-only in the host, the guest should obey */
--
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