tools/virtio: make vringh_test use inbuf/outbuf.

As expected, the simplified accessors are faster.

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 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@rustcorp.com.au>

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);

tools/virtio/vringh_test.c

@@ -369,11 +369,11 @@ static int parallel_test(unsigned long features,
 			 * user addr */
 			__kmalloc_fake = indirects + (xfers % RINGSIZE) * 4;
 			if (output)
-				err = virtqueue_add_buf(vq, sg, num_sg, 0, dbuf,
+				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) {
 				if (!virtqueue_enable_cb_delayed(vq))