[PATCH] rpmsg: char: Use preallocated SKBs.

[Piotr Wojtaszczyk]

On a message reception copy the message to a SKB taken from preallocated
pool instead of allocating a new SKB each time.
During high rpmsg traffic this reduces consumed CPU time noticeably.

Signed-off-by: Piotr Wojtaszczyk <piotr.wojtaszczyk@xxxxxxxxxxx>
---
 drivers/rpmsg/rpmsg_char.c       | 46 +++++++++++++++++++++++++++++---
 drivers/rpmsg/rpmsg_internal.h   | 21 +++++++++++++++
 drivers/rpmsg/virtio_rpmsg_bus.c | 21 ---------------
 3 files changed, 64 insertions(+), 24 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 3e0b8f3496ed..51b1b077687e 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -66,10 +66,37 @@ struct rpmsg_eptdev {
 
 	spinlock_t queue_lock;
 	struct sk_buff_head queue;
+	struct sk_buff_head skb_pool;
 	wait_queue_head_t readq;
 
 };
 
+static inline
+struct sk_buff *rpmsg_eptdev_get_skb(struct rpmsg_eptdev *eptdev)
+{
+	struct sk_buff *skb;
+
+	skb = skb_dequeue(&eptdev->skb_pool);
+	if (!skb)
+		skb = alloc_skb(MAX_RPMSG_BUF_SIZE, GFP_ATOMIC);
+	return skb;
+}
+
+static inline
+void rpmsg_eptdev_put_skb(struct rpmsg_eptdev *eptdev, struct sk_buff *skb)
+{
+	/* Recycle the skb */
+	skb->tail = 0;
+	skb->len = 0;
+	skb_queue_head(&eptdev->skb_pool, skb);
+}
+
+static void rpmsg_eptdev_free_all_skb(struct rpmsg_eptdev *eptdev)
+{
+	skb_queue_purge(&eptdev->queue);
+	skb_queue_purge(&eptdev->skb_pool);
+}
+
 int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 {
 	struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
@@ -99,7 +126,7 @@ static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
 	struct rpmsg_eptdev *eptdev = priv;
 	struct sk_buff *skb;
 
-	skb = alloc_skb(len, GFP_ATOMIC);
+	skb = rpmsg_eptdev_get_skb(eptdev);
 	if (!skb)
 		return -ENOMEM;
 
@@ -121,6 +148,18 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
 	struct rpmsg_endpoint *ept;
 	struct rpmsg_device *rpdev = eptdev->rpdev;
 	struct device *dev = &eptdev->dev;
+	struct sk_buff *skb;
+	int i;
+
+	/* Preallocate 8 SKBs */
+	for (i = 0; i < 8; i++) {
+		skb = rpmsg_eptdev_get_skb(eptdev);
+		if (!skb) {
+			rpmsg_eptdev_free_all_skb(eptdev);
+			return -ENOMEM;
+		}
+		rpmsg_eptdev_put_skb(eptdev, skb);
+	}
 
 	mutex_lock(&eptdev->ept_lock);
 	if (eptdev->ept) {
@@ -168,7 +207,7 @@ static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
 	mutex_unlock(&eptdev->ept_lock);
 
 	/* Discard all SKBs */
-	skb_queue_purge(&eptdev->queue);
+	rpmsg_eptdev_free_all_skb(eptdev);
 
 	put_device(dev);
 
@@ -217,7 +256,7 @@ static ssize_t rpmsg_eptdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	if (copy_to_iter(skb->data, use, to) != use)
 		use = -EFAULT;
 
-	kfree_skb(skb);
+	rpmsg_eptdev_put_skb(eptdev, skb);
 
 	return use;
 }
@@ -370,6 +409,7 @@ static struct rpmsg_eptdev *rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev
 	mutex_init(&eptdev->ept_lock);
 	spin_lock_init(&eptdev->queue_lock);
 	skb_queue_head_init(&eptdev->queue);
+	skb_queue_head_init(&eptdev->skb_pool);
 	init_waitqueue_head(&eptdev->readq);
 
 	device_initialize(dev);
diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
index 39b646d0d40d..b30bfe01db69 100644
--- a/drivers/rpmsg/rpmsg_internal.h
+++ b/drivers/rpmsg/rpmsg_internal.h
@@ -15,6 +15,27 @@
 #include <linux/rpmsg.h>
 #include <linux/poll.h>
 
+/*
+ * We're allocating buffers of 512 bytes each for communications. The
+ * number of buffers will be computed from the number of buffers supported
+ * by the vring, upto a maximum of 512 buffers (256 in each direction).
+ *
+ * Each buffer will have 16 bytes for the msg header and 496 bytes for
+ * the payload.
+ *
+ * This will utilize a maximum total space of 256KB for the buffers.
+ *
+ * We might also want to add support for user-provided buffers in time.
+ * This will allow bigger buffer size flexibility, and can also be used
+ * to achieve zero-copy messaging.
+ *
+ * Note that these numbers are purely a decision of this driver - we
+ * can change this without changing anything in the firmware of the remote
+ * processor.
+ */
+#define MAX_RPMSG_NUM_BUFS	(512)
+#define MAX_RPMSG_BUF_SIZE	(512)
+
 #define to_rpmsg_device(d) container_of(d, struct rpmsg_device, dev)
 #define to_rpmsg_driver(d) container_of(d, struct rpmsg_driver, drv)
 
diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
index 905ac7910c98..5369669d3327 100644
--- a/drivers/rpmsg/virtio_rpmsg_bus.c
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -109,27 +109,6 @@ struct virtio_rpmsg_channel {
 #define to_virtio_rpmsg_channel(_rpdev) \
 	container_of(_rpdev, struct virtio_rpmsg_channel, rpdev)
 
-/*
- * We're allocating buffers of 512 bytes each for communications. The
- * number of buffers will be computed from the number of buffers supported
- * by the vring, upto a maximum of 512 buffers (256 in each direction).
- *
- * Each buffer will have 16 bytes for the msg header and 496 bytes for
- * the payload.
- *
- * This will utilize a maximum total space of 256KB for the buffers.
- *
- * We might also want to add support for user-provided buffers in time.
- * This will allow bigger buffer size flexibility, and can also be used
- * to achieve zero-copy messaging.
- *
- * Note that these numbers are purely a decision of this driver - we
- * can change this without changing anything in the firmware of the remote
- * processor.
- */
-#define MAX_RPMSG_NUM_BUFS	(512)
-#define MAX_RPMSG_BUF_SIZE	(512)
-
 /*
  * Local addresses are dynamically allocated on-demand.
  * We do not dynamically assign addresses from the low 1024 range,
-- 
2.38.1