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Date: Thu, 7 Feb 2013 13:22:31 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Wanlong Gao <gaowanlong@...fujitsu.com>, asias@...hat.com,
Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: [RFC PATCH 7/8] virtio-scsi: use virtqueue_start_buf
Using the new virtio_scsi_add_sg function lets us simplify the queueing
path. In particular, all data protected by the tgt_lock is just gone
(multiqueue will find a new use for the lock).
The speedup is relatively small (2-4%) but it is worthwhile because of
the code simplification it enables. And it will be particularly useful
when adding multiqueue supoprt, because it keeps the tgt_lock critical
sections very slim while avoiding a proliferation of locks.
Signed-off-by: Wanlong Gao <gaowanlong@...fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
drivers/scsi/virtio_scsi.c | 103 +++++++++++++++++++-------------------------
1 files changed, 45 insertions(+), 58 deletions(-)
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 3449a1f..3b61173 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -59,11 +59,8 @@ struct virtio_scsi_vq {
/* Per-target queue state */
struct virtio_scsi_target_state {
- /* Protects sg. Lock hierarchy is tgt_lock -> vq_lock. */
+ /* Never held at the same time as vq_lock. */
spinlock_t tgt_lock;
-
- /* For sglist construction when adding commands to the virtqueue. */
- struct scatterlist sg[];
};
/* Driver instance state */
@@ -351,89 +348,83 @@ static void virtscsi_event_done(struct virtqueue *vq)
spin_unlock_irqrestore(&vscsi->event_vq.vq_lock, flags);
};
-static void virtscsi_map_sgl(struct scatterlist *sg, unsigned int *p_idx,
- struct scsi_data_buffer *sdb)
-{
- struct sg_table *table = &sdb->table;
- struct scatterlist *sg_elem;
- unsigned int idx = *p_idx;
- int i;
-
- for_each_sg(table->sgl, sg_elem, table->nents, i)
- sg[idx++] = *sg_elem;
-
- *p_idx = idx;
-}
-
/**
- * virtscsi_map_cmd - map a scsi_cmd to a virtqueue scatterlist
+ * virtscsi_add_cmd - add a virtio_scsi_cmd to a virtqueue
* @vscsi : virtio_scsi state
* @cmd : command structure
- * @out_num : number of read-only elements
- * @in_num : number of write-only elements
* @req_size : size of the request buffer
* @resp_size : size of the response buffer
- *
- * Called with tgt_lock held.
+ * @gfp : flags to use for memory allocations
*/
-static void virtscsi_map_cmd(struct virtio_scsi_target_state *tgt,
- struct virtio_scsi_cmd *cmd,
- unsigned *out_num, unsigned *in_num,
- size_t req_size, size_t resp_size)
+static int virtscsi_add_cmd(struct virtqueue *vq,
+ struct virtio_scsi_cmd *cmd,
+ size_t req_size, size_t resp_size, gfp_t gfp)
{
struct scsi_cmnd *sc = cmd->sc;
- struct scatterlist *sg = tgt->sg;
- unsigned int idx = 0;
+ struct scatterlist sg;
+ unsigned int count, count_sg;
+ struct sg_table *out, *in;
+ struct virtqueue_buf buf;
+ int ret;
+
+ out = in = NULL;
+
+ if (sc && sc->sc_data_direction != DMA_NONE) {
+ if (sc->sc_data_direction != DMA_FROM_DEVICE)
+ out = &scsi_out(sc)->table;
+ if (sc->sc_data_direction != DMA_TO_DEVICE)
+ in = &scsi_in(sc)->table;
+ }
+
+ count_sg = 2 + (out ? 1 : 0) + (in ? 1 : 0);
+ count = 2 + (out ? out->nents : 0) + (in ? in->nents : 0);
+ ret = virtqueue_start_buf(vq, &buf, cmd, count, count_sg, gfp);
+ if (ret < 0)
+ return ret;
/* Request header. */
- sg_set_buf(&sg[idx++], &cmd->req, req_size);
+ sg_init_one(&sg, &cmd->req, req_size);
+ virtqueue_add_sg_single(&buf, &sg, DMA_TO_DEVICE);
/* Data-out buffer. */
- if (sc && sc->sc_data_direction != DMA_FROM_DEVICE)
- virtscsi_map_sgl(sg, &idx, scsi_out(sc));
-
- *out_num = idx;
+ if (out)
+ virtqueue_add_sg(&buf, out->sgl, out->nents, DMA_TO_DEVICE);
/* Response header. */
- sg_set_buf(&sg[idx++], &cmd->resp, resp_size);
+ sg_init_one(&sg, &cmd->resp, resp_size);
+ virtqueue_add_sg_single(&buf, &sg, DMA_FROM_DEVICE);
/* Data-in buffer */
- if (sc && sc->sc_data_direction != DMA_TO_DEVICE)
- virtscsi_map_sgl(sg, &idx, scsi_in(sc));
+ if (in)
+ virtqueue_add_sg(&buf, in->sgl, in->nents, DMA_FROM_DEVICE);
- *in_num = idx - *out_num;
+ virtqueue_end_buf(&buf);
+ return 0;
}
-static int virtscsi_kick_cmd(struct virtio_scsi_target_state *tgt,
- struct virtio_scsi_vq *vq,
+static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
struct virtio_scsi_cmd *cmd,
size_t req_size, size_t resp_size, gfp_t gfp)
{
- unsigned int out_num, in_num;
unsigned long flags;
- int err;
+ int ret;
bool needs_kick = false;
- spin_lock_irqsave(&tgt->tgt_lock, flags);
- virtscsi_map_cmd(tgt, cmd, &out_num, &in_num, req_size, resp_size);
-
- spin_lock(&vq->vq_lock);
- err = virtqueue_add_buf(vq->vq, tgt->sg, out_num, in_num, cmd, gfp);
- spin_unlock(&tgt->tgt_lock);
- if (!err)
+ spin_lock_irqsave(&vq->vq_lock, flags);
+ ret = virtscsi_add_cmd(vq->vq, cmd, req_size, resp_size, gfp);
+ if (!ret)
needs_kick = virtqueue_kick_prepare(vq->vq);
spin_unlock_irqrestore(&vq->vq_lock, flags);
if (needs_kick)
virtqueue_notify(vq->vq);
- return err;
+ return ret;
}
static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
{
struct virtio_scsi *vscsi = shost_priv(sh);
- struct virtio_scsi_target_state *tgt = vscsi->tgt[sc->device->id];
struct virtio_scsi_cmd *cmd;
int ret;
@@ -467,7 +458,7 @@ 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(tgt, &vscsi->req_vq, cmd,
+ if (virtscsi_kick_cmd(&vscsi->req_vq, cmd,
sizeof cmd->req.cmd, sizeof cmd->resp.cmd,
GFP_ATOMIC) == 0)
ret = 0;
@@ -481,11 +472,10 @@ out:
static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
{
DECLARE_COMPLETION_ONSTACK(comp);
- struct virtio_scsi_target_state *tgt = vscsi->tgt[cmd->sc->device->id];
int ret = FAILED;
cmd->comp = ∁
- if (virtscsi_kick_cmd(tgt, &vscsi->ctrl_vq, cmd,
+ if (virtscsi_kick_cmd(&vscsi->ctrl_vq, cmd,
sizeof cmd->req.tmf, sizeof cmd->resp.tmf,
GFP_NOIO) < 0)
goto out;
@@ -592,14 +582,11 @@ static struct virtio_scsi_target_state *virtscsi_alloc_tgt(
gfp_t gfp_mask = GFP_KERNEL;
/* We need extra sg elements at head and tail. */
- tgt = kmalloc(sizeof(*tgt) + sizeof(tgt->sg[0]) * (sg_elems + 2),
- gfp_mask);
-
+ tgt = kmalloc(sizeof(*tgt), gfp_mask);
if (!tgt)
return NULL;
spin_lock_init(&tgt->tgt_lock);
- sg_init_table(tgt->sg, sg_elems + 2);
return tgt;
}
--
1.7.1
--
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