Linux Virtualization - Jan 2010 - [PATCH 0/2] virtio net improvements

Hi Dave,

   Nice driver optimization from Shirley, but requires a new virtio hook.
Do you want to take both?  I have nothing else overlapping it.

Cheers,
Rusty.

From: Shirley Ma <mashirle at us.ibm.com>

There's currently no way for a virtio driver to ask for unused
buffers, so it has to keep a list itself to reclaim them at shutdown.
This is redundant, since virtio_ring stores that information.  So
add a new hook to do this.

Signed-off-by: Shirley Ma <xma at us.ibm.com>
Signed-off-by: Amit Shah <amit.shah at redhat.com>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
---
 drivers/virtio/virtio_ring.c |   25 +++++++++++++++++++++++++
 include/linux/virtio.h       |    4 ++++
 2 files changed, 29 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fbd2ecd..71929ee 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -334,6 +334,30 @@ static bool vring_enable_cb(struct virtqueue *_vq)
 	return true;
 }
 
+static void *vring_detach_unused_buf(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	unsigned int i;
+	void *buf;
+
+	START_USE(vq);
+
+	for (i = 0; i < vq->vring.num; i++) {
+		if (!vq->data[i])
+			continue;
+		/* detach_buf clears data, so grab it now. */
+		buf = vq->data[i];
+		detach_buf(vq, i);
+		END_USE(vq);
+		return buf;
+	}
+	/* That should have freed everything. */
+	BUG_ON(vq->num_free != vq->vring.num);
+
+	END_USE(vq);
+	return NULL;
+}
+
 irqreturn_t vring_interrupt(int irq, void *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
@@ -360,6 +384,7 @@ static struct virtqueue_ops vring_vq_ops = {
 	.kick = vring_kick,
 	.disable_cb = vring_disable_cb,
 	.enable_cb = vring_enable_cb,
+	.detach_unused_buf = vring_detach_unused_buf,
 };
 
 struct virtqueue *vring_new_virtqueue(unsigned int num,
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 057a2e0..f508c65 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -51,6 +51,9 @@ struct virtqueue {
  *	This re-enables callbacks; it returns "false" if there are pending
  *	buffers in the queue, to detect a possible race between the driver
  *	checking for more work, and enabling callbacks.
+ * @detach_unused_buf: detach first unused buffer
+ * 	vq: the struct virtqueue we're talking about.
+ * 	Returns NULL or the "data" token handed to add_buf
  *
  * Locking rules are straightforward: the driver is responsible for
  * locking.  No two operations may be invoked simultaneously, with the
exception
@@ -71,6 +74,7 @@ struct virtqueue_ops {
 
 	void (*disable_cb)(struct virtqueue *vq);
 	bool (*enable_cb)(struct virtqueue *vq);
+	void *(*detach_unused_buf)(struct virtqueue *vq);
 };
 
 /**

On Fri, 29 Jan 2010 11:46:43 pm Rusty Russell wrote:
> Hi Dave,
> 
>    Nice driver optimization from Shirley, but requires a new virtio hook.
> Do you want to take both?  I have nothing else overlapping it.
Dave, any news on this?  Shirley, I note that your final commit message did
not contain this information from your original version:

	Tests have been done for small packets, big packets and
	mergeable buffers.

	The single netperf TCP_STREAM performance improved for host to guest. 
	It also reduces UDP packets drop rate.

	The netperf laptop results were:

	mtu=1500
	netperf -H xxx -l 120

	                w/o patch       w/i patch (two runs)    
	guest to host:  3336.84Mb/s   3730.14Mb/s ~ 3582.88Mb/s

	host to guest:  3165.10Mb/s   3370.39Mb/s ~ 3407.96Mb/s

Thanks,
Rusty.

From: Rusty Russell <rusty at rustcorp.com.au>
Date: Wed, 3 Feb 2010 09:57:06 +1030
> On Fri, 29 Jan 2010 11:46:43 pm Rusty Russell wrote:
>> Hi Dave,
>> 
>>    Nice driver optimization from Shirley, but requires a new virtio
hook.
>> Do you want to take both?  I have nothing else overlapping it.
> 
> Dave, any news on this?
Just slowly creeping up the backlog :-)