Linux Virtualization - May 2011 - [PATCH RFC] virtio_net: fix patch: virtio_net: limit xmit polling

The patch  virtio_net: limit xmit polling
got the logic reversed: it polled while we had
capacity not while ring was empty.

Fix it up and clean up a bit by using a for loop.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---

OK, turns out that patch was borken. Here's
a fix that survived stress test on my box.
Pushed on my branch, I'll send a rebased series
with Rusty's comments addressed ASAP.

 drivers/net/virtio_net.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9982bd7..c8cd22d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -514,12 +514,14 @@ static bool free_old_xmit_skbs(struct virtnet_info *vi,
int capacity)
 	struct sk_buff *skb;
 	unsigned int len;
 	bool c;
+	int n;
+
 	/* We try to free up at least 2 skbs per one sent, so that we'll get
 	 * all of the memory back if they are used fast enough. */
-	int n = 2;
-
-	while ((c = virtqueue_get_capacity(vi->svq) >= capacity) && --n
> 0 &&
-	       (skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
+	for (n = 0;
+	     ((c = virtqueue_get_capacity(vi->svq)) < capacity || n < 2)
&&
+	     ((skb = virtqueue_get_buf(vi->svq, &len)));
+	     ++n) {
 		pr_debug("Sent skb %p\n", skb);
 		vi->dev->stats.tx_bytes += skb->len;
 		vi->dev->stats.tx_packets++;
-- 
1.7.5.53.gc233e

On Thu, 19 May 2011 01:01:25 +0300, "Michael S. Tsirkin" <mst at
redhat.com> wrote:
> The patch  virtio_net: limit xmit polling
> got the logic reversed: it polled while we had
> capacity not while ring was empty.
> 
> Fix it up and clean up a bit by using a for loop.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
> 
> OK, turns out that patch was borken. Here's
> a fix that survived stress test on my box.
> Pushed on my branch, I'll send a rebased series
> with Rusty's comments addressed ASAP.
Normally you would have missed the merge window by now, but I'd really
like this stuff in, so I'm holding it open for this.  I want these patches
in linux-next for at least a few days before I push them.

If you think we're not close enough, please tell me and I'll push
the rest of the virtio patches to Linus now.  

Thanks,
Rusty.