lkml.org 
[lkml]   [2011]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCHv2 RFC 0/4] virtio and vhost-net capacity handling
On Thu, Jun 02, 2011 at 06:42:35PM +0300, Michael S. Tsirkin wrote:
> OK, here's a new attempt to use the new capacity api. I also added more
> comments to clarify the logic. Hope this is more readable. Let me know
> pls.
>
> This is on top of the patches applied by Rusty.
>
> Warning: untested. Posting now to give people chance to
> comment on the API.
>
> Changes from v1:
> - fix comment in patch 2 to correct confusion noted by Rusty
> - rewrite patch 3 along the lines suggested by Rusty
> note: it's not exactly the same but I hope it's close
> enough, the main difference is that mine does limited
> polling even in the unlikely xmit failure case.
> - added a patch to not return capacity from add_buf
> it always looked like a weird hack
>
> Michael S. Tsirkin (4):
> virtio_ring: add capacity check API
> virtio_net: fix tx capacity checks using new API
> virtio_net: limit xmit polling
> Revert "virtio: make add_buf return capacity remaining:
>
> drivers/net/virtio_net.c | 111 ++++++++++++++++++++++++++----------------
> drivers/virtio/virtio_ring.c | 10 +++-
> include/linux/virtio.h | 7 ++-
> 3 files changed, 84 insertions(+), 44 deletions(-)
>
> --
> 1.7.5.53.gc233e


And just FYI, here's a patch (on top) that I considered but
decided against. This does a single get_buf before
xmit. I thought it's not really needed as the capacity
check in add_buf is relatively cheap, and we removed
the kick in xmit_skb. But the point is that the loop
will now be easy to move around if someone manages
to show this benefits speed (which I doubt).

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b25db1c..75af5be 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -590,6 +590,9 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
struct virtnet_info *vi = netdev_priv(dev);
int ret, i;

+ /* Try to pop an skb, to increase the chance we can add this one. */
+ free_old_xmit_skb(v);
+
/* We normally do have space in the ring, so try to queue the skb as
* fast as possible. */
ret = xmit_skb(vi, skb);
@@ -627,8 +630,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
* This is so that we don't hog the skb memory unnecessarily. *
* Doing this after kick means there's a chance we'll free
* the skb we have just sent, which is hot in cache. */
- for (i = 0; i < 2; i++)
- free_old_xmit_skb(v);
+ free_old_xmit_skb(v);

if (likely(free_xmit_capacity(vi)))
return NETDEV_TX_OK;

\
 
 \ /
  Last update: 2011-06-02 19:19    [W:0.313 / U:1.948 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site