virtio_ring: virtqueue_add_sgs, to add multiple sgs.

virtio_scsi can really use this, to avoid the current hack of copying
the whole sg array.  Some other things get slightly neater, too.

This causes a slowdown in virtqueue_add_buf(), which is implemented as
a wrapper.  This is addressed in the next patches.

for i in `seq 50`; do /usr/bin/time -f 'Wall time:%e' ./vringh_test --indirect --eventidx --parallel --fast-vringh; done 2>&1 | stats --trim-outliers:

Before:
	Using CPUS 0 and 3
	Guest: notified 0, pinged 39009-39063(39062)
	Host: notified 39009-39063(39062), pinged 0
	Wall time:1.700000-1.950000(1.723542)

After:
	Using CPUS 0 and 3
	Guest: notified 0, pinged 39062-39063(39063)
	Host: notified 39062-39063(39063), pinged 0
	Wall time:1.760000-2.220000(1.789167)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Reviewed-by: Asias He <asias@redhat.com>

1 files changed, 157 insertions, 63 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 245177c286ae..a78ad459cc85 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -98,16 +98,36 @@ struct vring_virtqueue
 
 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 
+static inline struct scatterlist *sg_next_chained(struct scatterlist *sg,
+                                                  unsigned int *count)
+{
+        return sg_next(sg);
+}
+
+static inline struct scatterlist *sg_next_arr(struct scatterlist *sg,
+                                              unsigned int *count)
+{
+        if (--(*count) == 0)
+                return NULL;
+        return sg + 1;
+}
+
 /* Set up an indirect table of descriptors and add it to the queue. */
-static int vring_add_indirect(struct vring_virtqueue *vq,
-                              struct scatterlist sg[],
-                              unsigned int out,
-                              unsigned int in,
-                              gfp_t gfp)
+static inline int vring_add_indirect(struct vring_virtqueue *vq,
+                                     struct scatterlist *sgs[],
+                                     struct scatterlist *(*next)
+                                       (struct scatterlist *, unsigned int *),
+                                     unsigned int total_sg,
+                                     unsigned int total_out,
+                                     unsigned int total_in,
+                                     unsigned int out_sgs,
+                                     unsigned int in_sgs,
+                                     gfp_t gfp)
 {
         struct vring_desc *desc;
         unsigned head;
-        int i;
+        struct scatterlist *sg;
+        int i, n;
 
         /*
          * We require lowmem mappings for the descriptors because
@@ -116,25 +136,31 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
          */
         gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
 
-        desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
+        desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
         if (!desc)
                 return -ENOMEM;
 
-        /* Transfer entries from the sg list into the indirect page */
-        for (i = 0; i < out; i++) {
-                desc[i].flags = VRING_DESC_F_NEXT;
-                desc[i].addr = sg_phys(sg);
-                desc[i].len = sg->length;
-                desc[i].next = i+1;
-                sg++;
+        /* Transfer entries from the sg lists into the indirect page */
+        i = 0;
+        for (n = 0; n < out_sgs; n++) {
+                for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
+                        desc[i].flags = VRING_DESC_F_NEXT;
+                        desc[i].addr = sg_phys(sg);
+                        desc[i].len = sg->length;
+                        desc[i].next = i+1;
+                        i++;
+                }
         }
-        for (; i < (out + in); i++) {
-                desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
-                desc[i].addr = sg_phys(sg);
-                desc[i].len = sg->length;
-                desc[i].next = i+1;
-                sg++;
+        for (; n < (out_sgs + in_sgs); n++) {
+                for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
+                        desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
+                        desc[i].addr = sg_phys(sg);
+                        desc[i].len = sg->length;
+                        desc[i].next = i+1;
+                        i++;
+                }
         }
+        BUG_ON(i != total_sg);
 
         /* Last one doesn't continue. */
         desc[i-1].flags &= ~VRING_DESC_F_NEXT;
@@ -155,29 +181,20 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
         return head;
 }
 
-/**
- * virtqueue_add_buf - expose buffer to other end
- * @vq: the struct virtqueue we're talking about.
- * @sg: the description of the buffer(s).
- * @out_num: the number of sg readable by other side
- * @in_num: the number of sg which are writable (after readable ones)
- * @data: the token identifying the buffer.
- * @gfp: how to do memory allocations (if necessary).
- *
- * Caller must ensure we don't call this with other virtqueue operations
- * at the same time (except where noted).
- *
- * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
- */
-int virtqueue_add_buf(struct virtqueue *_vq,
-                      struct scatterlist sg[],
-                      unsigned int out,
-                      unsigned int in,
-                      void *data,
-                      gfp_t gfp)
+static inline int virtqueue_add(struct virtqueue *_vq,
+                                struct scatterlist *sgs[],
+                                struct scatterlist *(*next)
+                                  (struct scatterlist *, unsigned int *),
+                                unsigned int total_out,
+                                unsigned int total_in,
+                                unsigned int out_sgs,
+                                unsigned int in_sgs,
+                                void *data,
+                                gfp_t gfp)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
-        unsigned int i, avail, uninitialized_var(prev);
+        struct scatterlist *sg;
+        unsigned int i, n, avail, uninitialized_var(prev), total_sg;
         int head;
 
         START_USE(vq);
@@ -197,46 +214,54 @@ int virtqueue_add_buf(struct virtqueue *_vq,
         }
 #endif
 
+        total_sg = total_in + total_out;
+
         /* If the host supports indirect descriptor tables, and we have multiple
          * buffers, then go indirect. FIXME: tune this threshold */
-        if (vq->indirect && (out + in) > 1 && vq->vq.num_free) {
-                head = vring_add_indirect(vq, sg, out, in, gfp);
+        if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
+                head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
+                                          total_in,
+                                          out_sgs, in_sgs, gfp);
                 if (likely(head >= 0))
                         goto add_head;
         }
 
-        BUG_ON(out + in > vq->vring.num);
-        BUG_ON(out + in == 0);
+        BUG_ON(total_sg > vq->vring.num);
+        BUG_ON(total_sg == 0);
 
-        if (vq->vq.num_free < out + in) {
+        if (vq->vq.num_free < total_sg) {
                 pr_debug("Can't add buf len %i - avail = %i\n",
-                         out + in, vq->vq.num_free);
+                         total_sg, vq->vq.num_free);
                 /* FIXME: for historical reasons, we force a notify here if
                  * there are outgoing parts to the buffer.  Presumably the
                  * host should service the ring ASAP. */
-                if (out)
+                if (out_sgs)
                         vq->notify(&vq->vq);
                 END_USE(vq);
                 return -ENOSPC;
         }
 
         /* We're about to use some buffers from the free list. */
-        vq->vq.num_free -= out + in;
-
-        head = vq->free_head;
-        for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
-                vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
-                vq->vring.desc[i].addr = sg_phys(sg);
-                vq->vring.desc[i].len = sg->length;
-                prev = i;
-                sg++;
+        vq->vq.num_free -= total_sg;
+
+        head = i = vq->free_head;
+        for (n = 0; n < out_sgs; n++) {
+                for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
+                        vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
+                        vq->vring.desc[i].addr = sg_phys(sg);
+                        vq->vring.desc[i].len = sg->length;
+                        prev = i;
+                        i = vq->vring.desc[i].next;
+                }
         }
-        for (; in; i = vq->vring.desc[i].next, in--) {
-                vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
-                vq->vring.desc[i].addr = sg_phys(sg);
-                vq->vring.desc[i].len = sg->length;
-                prev = i;
-                sg++;
+        for (; n < (out_sgs + in_sgs); n++) {
+                for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
+                        vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
+                        vq->vring.desc[i].addr = sg_phys(sg);
+                        vq->vring.desc[i].len = sg->length;
+                        prev = i;
+                        i = vq->vring.desc[i].next;
+                }
         }
         /* Last one doesn't continue. */
         vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
@@ -269,9 +294,78 @@ add_head:
 
         return 0;
 }
+
+/**
+ * virtqueue_add_buf - expose buffer to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sg: the description of the buffer(s).
+ * @out_num: the number of sg readable by other side
+ * @in_num: the number of sg which are writable (after readable ones)
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
+ */
+int virtqueue_add_buf(struct virtqueue *_vq,
+                      struct scatterlist sg[],
+                      unsigned int out,
+                      unsigned int in,
+                      void *data,
+                      gfp_t gfp)
+{
+        struct scatterlist *sgs[2];
+
+        sgs[0] = sg;
+        sgs[1] = sg + out;
+
+        return virtqueue_add(_vq, sgs, sg_next_arr,
+                             out, in, out ? 1 : 0, in ? 1 : 0, data, gfp);
+}
 EXPORT_SYMBOL_GPL(virtqueue_add_buf);
 
 /**
+ * virtqueue_add_sgs - expose buffers to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of terminated scatterlists.
+ * @out_num: the number of scatterlists readable by other side
+ * @in_num: the number of scatterlists which are writable (after readable ones)
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
+ */
+int virtqueue_add_sgs(struct virtqueue *_vq,
+                      struct scatterlist *sgs[],
+                      unsigned int out_sgs,
+                      unsigned int in_sgs,
+                      void *data,
+                      gfp_t gfp)
+{
+        unsigned int i, total_out, total_in;
+
+        /* Count them first. */
+        for (i = total_out = total_in = 0; i < out_sgs; i++) {
+                struct scatterlist *sg;
+                for (sg = sgs[i]; sg; sg = sg_next(sg))
+                        total_out++;
+        }
+        for (; i < out_sgs + in_sgs; i++) {
+                struct scatterlist *sg;
+                for (sg = sgs[i]; sg; sg = sg_next(sg))
+                        total_in++;
+        }
+        return virtqueue_add(_vq, sgs, sg_next_chained,
+                             total_out, total_in, out_sgs, in_sgs, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
+
+/**
  * virtqueue_kick_prepare - first half of split virtqueue_kick call.
  * @vq: the struct virtqueue
  *