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Rusty Russell

2013-Mar-06 05:15 UTC

[PATCH 0/6] virtio_add_buf replacement.

OK, so I've spent a few days benchmarking.  Turns out 80% of
virtio_add_buf cases are uni-directional (including the
always-performance-sensitive networking code), and that gets no
performance penalty (though tests with real networking would be
appreciated!).

I'm not reposting all the "convert driver to virtio_add_outbuf()"
patches: just the scsi one which I didn't have before.  I won't actually
remove virtio_add_buf() until the *following* merge window, just to be
sure.

One annoying thing about benchmarking is that in some cases, speeding up
one side can make the whole thing slower, due to more wakeups.
Device-side polling techniques might be required in future to get more
performance.

Cheers,
Rusty.

Rusty Russell

2013-Mar-06 05:19 UTC

head link

[PATCH 1/6] 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 naively
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 39019-39063(39061)
	Host: notified 39019-39063(39061), pinged 0
	Wall time:2.090000-2.520000(2.188542)

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

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 245177c..27e31d3 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -100,14 +100,16 @@ struct vring_virtqueue
 
 /* 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,
+			      struct scatterlist *sgs[],
+			      unsigned int total_sg,
+			      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 +118,31 @@ 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 = sg_next(sg)) {
+			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 = sg_next(sg)) {
+			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;
@@ -176,8 +184,48 @@ int virtqueue_add_buf(struct virtqueue *_vq,
 		      void *data,
 		      gfp_t gfp)
 {
+	struct scatterlist *sgs[2];
+	unsigned int i;
+
+	sgs[0] = sg;
+	sgs[1] = sg + out;
+
+	/* Workaround until callers pass well-formed sgs. */
+	for (i = 0; i < out + in; i++)
+		sg_unmark_end(sg + i);
+
+	sg_mark_end(sg + out + in - 1);
+	if (out && in)
+		sg_mark_end(sg + out - 1);
+
+	return virtqueue_add_sgs(_vq, sgs, 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)
+{
 	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 +245,58 @@ int virtqueue_add_buf(struct virtqueue *_vq,
 	}
 #endif
 
+	/* Count them first. */
+	for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
+		struct scatterlist *sg;
+		for (sg = sgs[i]; sg; sg = sg_next(sg))
+			total_sg++;
+	}
+
 	/* 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, total_sg, 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 = sg_next(sg)) {
+			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 = sg_next(sg)) {
+			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;
@@ -269,7 +329,7 @@ add_head:
 
 	return 0;
 }
-EXPORT_SYMBOL_GPL(virtqueue_add_buf);
+EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
 
 /**
  * virtqueue_kick_prepare - first half of split virtqueue_kick call.
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index ff6714e..6eff15b 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -40,6 +40,13 @@ int virtqueue_add_buf(struct virtqueue *vq,
 		      void *data,
 		      gfp_t gfp);
 
+int virtqueue_add_sgs(struct virtqueue *vq,
+		      struct scatterlist *sgs[],
+		      unsigned int out_sgs,
+		      unsigned int in_sgs,
+		      void *data,
+		      gfp_t gfp);
+
 void virtqueue_kick(struct virtqueue *vq);
 
 bool virtqueue_kick_prepare(struct virtqueue *vq);
diff --git a/tools/virtio/linux/scatterlist.h b/tools/virtio/linux/scatterlist.h
index b2cf7d0..68c9e2a 100644
--- a/tools/virtio/linux/scatterlist.h
+++ b/tools/virtio/linux/scatterlist.h
@@ -125,6 +125,22 @@ static inline void sg_mark_end(struct scatterlist *sg)
 	sg->page_link &= ~0x01;
 }
 
+/**
+ * sg_unmark_end - Undo setting the end of the scatterlist
+ * @sg:		 SG entryScatterlist
+ *
+ * Description:
+ *   Removes the termination marker from the given entry of the scatterlist.
+ *
+ **/
+static inline void sg_unmark_end(struct scatterlist *sg)
+{
+#ifdef CONFIG_DEBUG_SG
+	BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+	sg->page_link &= ~0x02;
+}
+
 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 {
 #ifdef CONFIG_DEBUG_SG
diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h
index e4af659..5fa612a 100644
--- a/tools/virtio/linux/virtio.h
+++ b/tools/virtio/linux/virtio.h
@@ -56,6 +56,13 @@ int virtqueue_add_buf(struct virtqueue *vq,
 		      void *data,
 		      gfp_t gfp);
 
+int virtqueue_add_sgs(struct virtqueue *vq,
+		      struct scatterlist *sgs[],
+		      unsigned int out_sgs,
+		      unsigned int in_sgs,
+		      void *data,
+		      gfp_t gfp);
+
 void virtqueue_kick(struct virtqueue *vq);
 
 void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);

Rusty Russell

2013-Mar-06 05:20 UTC

head link

[PATCH 2/6] virtio_ring: don't count elements twice for add_buf path.

Extract the post-counting code into virtqueue_add(), make both callers
use it.  As much for neatness as optimization.

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 39019-39063(39061)
	Host: notified 39019-39063(39061), pinged 0
	Wall time:2.090000-2.520000(2.188542)

After:
	Using CPUS 0 and 3
	Guest: notified 0, pinged 39014-39063(39062)
	Host: notified 39014-39063(39062), pinged 0
	Wall time:1.900000-2.350000(1.921875)

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au> 
Reviewed-by: Wanlong Gao <gaowanlong at cn.fujitsu.com>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 27e31d3..c537385 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -163,69 +163,17 @@ 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)
-{
-	struct scatterlist *sgs[2];
-	unsigned int i;
-
-	sgs[0] = sg;
-	sgs[1] = sg + out;
-
-	/* Workaround until callers pass well-formed sgs. */
-	for (i = 0; i < out + in; i++)
-		sg_unmark_end(sg + i);
-
-	sg_mark_end(sg + out + in - 1);
-	if (out && in)
-		sg_mark_end(sg + out - 1);
-
-	return virtqueue_add_sgs(_vq, sgs, 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)
+static int virtqueue_add(struct virtqueue *_vq,
+			 struct scatterlist *sgs[],
+			 unsigned int total_sg,
+			 unsigned int out_sgs,
+			 unsigned int in_sgs,
+			 void *data,
+			 gfp_t gfp)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct scatterlist *sg;
-	unsigned int i, n, avail, uninitialized_var(prev), total_sg;
+	unsigned int i, n, avail, uninitialized_var(prev);
 	int head;
 
 	START_USE(vq);
@@ -245,13 +193,6 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
 	}
 #endif
 
-	/* Count them first. */
-	for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
-		struct scatterlist *sg;
-		for (sg = sgs[i]; sg; sg = sg_next(sg))
-			total_sg++;
-	}
-
 	/* If the host supports indirect descriptor tables, and we have multiple
 	 * buffers, then go indirect. FIXME: tune this threshold */
 	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
{
@@ -329,6 +270,78 @@ 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];
+	unsigned int i;
+
+	sgs[0] = sg;
+	sgs[1] = sg + out;
+
+	/* Workaround until callers pass well-formed sgs. */
+	for (i = 0; i < out + in; i++)
+		sg_unmark_end(sg + i);
+
+	sg_mark_end(sg + out + in - 1);
+	if (out && in)
+		sg_mark_end(sg + out - 1);
+
+	return virtqueue_add(_vq, sgs, 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_sg;
+
+	/* Count them first. */
+	for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
+		struct scatterlist *sg;
+		for (sg = sgs[i]; sg; sg = sg_next(sg))
+			total_sg++;
+	}
+	return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs, data, gfp);
+}
 EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
 
 /**

Rusty Russell

2013-Mar-06 05:22 UTC

head link

[PATCH 3/6] virtio_ring: inline internal vring functions more aggressively.

We use inline and get gcc to do the right thing inlining the
"indirect" traversal functions.  This also means we don't need to
clean the sgs.

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 39014-39063(39062)
	Host: notified 39014-39063(39062), pinged 0
	Wall time:1.900000-2.350000(1.921875)

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 at rustcorp.com.au> 

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c537385..a78ad45 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -98,13 +98,31 @@ 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 *sgs[],
-			      unsigned int total_sg,
-			      unsigned int out_sgs,
-			      unsigned int in_sgs,
-			      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;
@@ -125,7 +143,7 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
 	/* 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 = sg_next(sg)) {
+		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;
@@ -134,7 +152,7 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
 		}
 	}
 	for (; n < (out_sgs + in_sgs); n++) {
-		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+		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;
@@ -163,17 +181,20 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
 	return head;
 }
 
-static int virtqueue_add(struct virtqueue *_vq,
-			 struct scatterlist *sgs[],
-			 unsigned int total_sg,
-			 unsigned int out_sgs,
-			 unsigned int in_sgs,
-			 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);
 	struct scatterlist *sg;
-	unsigned int i, n, avail, uninitialized_var(prev);
+	unsigned int i, n, avail, uninitialized_var(prev), total_sg;
 	int head;
 
 	START_USE(vq);
@@ -193,11 +214,14 @@ static int virtqueue_add(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 && total_sg > 1 && vq->vq.num_free)
{
-		head = vring_add_indirect(vq, sgs, total_sg, out_sgs, in_sgs,
-					  gfp);
+		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;
 	}
@@ -222,7 +246,7 @@ static int virtqueue_add(struct virtqueue *_vq,
 
 	head = i = vq->free_head;
 	for (n = 0; n < out_sgs; n++) {
-		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+		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;
@@ -231,7 +255,7 @@ static int virtqueue_add(struct virtqueue *_vq,
 		}
 	}
 	for (; n < (out_sgs + in_sgs); n++) {
-		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+		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;
@@ -293,21 +317,12 @@ int virtqueue_add_buf(struct virtqueue *_vq,
 		      gfp_t gfp)
 {
 	struct scatterlist *sgs[2];
-	unsigned int i;
 
 	sgs[0] = sg;
 	sgs[1] = sg + out;
 
-	/* Workaround until callers pass well-formed sgs. */
-	for (i = 0; i < out + in; i++)
-		sg_unmark_end(sg + i);
-
-	sg_mark_end(sg + out + in - 1);
-	if (out && in)
-		sg_mark_end(sg + out - 1);
-
-	return virtqueue_add(_vq, sgs, out+in, out ? 1 : 0, in ? 1 : 0,
-			     data, gfp);
+	return virtqueue_add(_vq, sgs, sg_next_arr,
+			     out, in, out ? 1 : 0, in ? 1 : 0, data, gfp);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_buf);
 
@@ -332,15 +347,21 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
 		      void *data,
 		      gfp_t gfp)
 {
-	unsigned int i, total_sg;
+	unsigned int i, total_out, total_in;
 
 	/* Count them first. */
-	for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
+	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_sg++;
+			total_in++;
 	}
-	return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs, data, gfp);
+	return virtqueue_add(_vq, sgs, sg_next_chained,
+			     total_out, total_in, out_sgs, in_sgs, data, gfp);
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_sgs);

Rusty Russell

2013-Mar-06 05:23 UTC

head link

[PATCH 4/6] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf.

These are specialized versions of virtqueue_add_buf(), which cover
over 80% of cases and are far clearer.

In particular, the scatterlists passed to these functions don't have
to be clean (ie. we ignore end markers).

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au> 

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a78ad45..5217baf 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -366,6 +366,50 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
 EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
 
 /**
+ * virtqueue_add_outbuf - expose output buffers to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists readable by other side
+ * @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_outbuf(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp)
+{
+	return virtqueue_add(vq, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
+
+/**
+ * virtqueue_add_inbuf - expose input buffers to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists writable by other side
+ * @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_inbuf(struct virtqueue *vq,
+			struct scatterlist sg[], unsigned int num,
+			void *data,
+			gfp_t gfp)
+{
+	return virtqueue_add(vq, &sg, sg_next_arr, 0, num, 0, 1, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
+
+/**
  * virtqueue_kick_prepare - first half of split virtqueue_kick call.
  * @vq: the struct virtqueue
  *
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 6eff15b..b442500 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -40,6 +40,16 @@ int virtqueue_add_buf(struct virtqueue *vq,
 		      void *data,
 		      gfp_t gfp);
 
+int virtqueue_add_outbuf(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp);
+
+int virtqueue_add_inbuf(struct virtqueue *vq,
+			struct scatterlist sg[], unsigned int num,
+			void *data,
+			gfp_t gfp);
+
 int virtqueue_add_sgs(struct virtqueue *vq,
 		      struct scatterlist *sgs[],
 		      unsigned int out_sgs,

Rusty Russell

2013-Mar-06 05:24 UTC

head link

[PATCH 5/6] tools/virtio: make vringh_test use inbuf/outbuf.

The simplified accessors are faster.

Before:
	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)

After:
	Using CPUS 0 and 3
	Guest: notified 0, pinged 39037-39063(39062)
	Host: notified 39037-39063(39062), pinged 0
	Wall time:1.640000-1.810000(1.676875)

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h
index 5fa612a..6df181a 100644
--- a/tools/virtio/linux/virtio.h
+++ b/tools/virtio/linux/virtio.h
@@ -63,6 +63,16 @@ int virtqueue_add_sgs(struct virtqueue *vq,
 		      void *data,
 		      gfp_t gfp);
 
+int virtqueue_add_outbuf(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp);
+
+int virtqueue_add_inbuf(struct virtqueue *vq,
+			struct scatterlist sg[], unsigned int num,
+			void *data,
+			gfp_t gfp);
+
 void virtqueue_kick(struct virtqueue *vq);
 
 void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c
index 7fedde8..cf33672 100644
--- a/tools/virtio/vringh_test.c
+++ b/tools/virtio/vringh_test.c
@@ -342,11 +342,11 @@ static int parallel_test(unsigned long features,
 			 * user addr */
 			__kmalloc_fake = indirects + (xfers % RINGSIZE) * 3;
 			if (output)
-				err = virtqueue_add_buf(vq, sg, num_sg, 0, dbuf,
-							GFP_KERNEL);
+				err = virtqueue_add_outbuf(vq, sg, num_sg, dbuf,
+							   GFP_KERNEL);
 			else
-				err = virtqueue_add_buf(vq, sg, 0, num_sg, dbuf,
-							GFP_KERNEL);
+				err = virtqueue_add_inbuf(vq, sg, num_sg,
+							  dbuf, GFP_KERNEL);
 
 			if (err == -ENOSPC) {
 				char buf[128];

Rusty Russell

2013-Mar-06 05:24 UTC

head link

[PATCH 6/6] virtio_scsi: use virtqueue_add_inbuf() for virtscsi_kick_event.

It's a bit clearer, and add_buf is going away.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index bae0c95..612e320 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -220,8 +220,8 @@ static int virtscsi_kick_event(struct virtio_scsi *vscsi,
 
 	spin_lock_irqsave(&vscsi->event_vq.vq_lock, flags);
 
-	err = virtqueue_add_buf(vscsi->event_vq.vq, &sg, 0, 1, event_node,
-				GFP_ATOMIC);
+	err = virtqueue_add_inbuf(vscsi->event_vq.vq, &sg, 1, event_node,
+				  GFP_ATOMIC);
 	if (!err)
 		virtqueue_kick(vscsi->event_vq.vq);

Asias He

2013-Mar-06 08:09 UTC

head link

[PATCH 0/6] virtio_add_buf replacement.

On Wed, Mar 06, 2013 at 04:15:02PM +1100, Rusty Russell
wrote:> OK, so I've spent a few days benchmarking.  Turns out 80% of
> virtio_add_buf cases are uni-directional (including the
> always-performance-sensitive networking code), and that gets no
> performance penalty (though tests with real networking would be
> appreciated!).
> 
> I'm not reposting all the "convert driver to
virtio_add_outbuf()"
> patches: just the scsi one which I didn't have before.  I won't
actually
> remove virtio_add_buf() until the *following* merge window, just to be
> sure.
Why not send out all the patches in this series? It would be much easier
for people to read in one thread.
> One annoying thing about benchmarking is that in some cases, speeding up
> one side can make the whole thing slower, due to more wakeups.
> Device-side polling techniques might be required in future to get more
> performance.
> 
> Cheers,
> Rusty.
> _______________________________________________
> Virtualization mailing list
> Virtualization at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization
-- 
Asias

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Virtualization - Mar 2013 - [PATCH 0/6] virtio_add_buf replacement.

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[PATCH 2/6] virtio_ring: don't count elements twice for add_buf path.

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[PATCH 4/6] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf.

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