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authorMark McLoughlin <markmc@redhat.com>2008-11-16 22:41:34 -0800
committerDavid S. Miller <davem@davemloft.net>2008-11-16 22:41:34 -0800
commit3f2c31d90327f21d76d296af34aa4ca547932ff4 (patch)
treefbcccc1ab9af94982dd2a98fae6b32c7a0e14e3a /include
parent0276b4972e932ea8bf2941dcd37e9caac5652ed7 (diff)
downloadlinux-3f2c31d90327f21d76d296af34aa4ca547932ff4.tar.bz2
virtio_net: VIRTIO_NET_F_MSG_RXBUF (imprive rcv buffer allocation)
If segmentation offload is enabled by the host, we currently allocate maximum sized packet buffers and pass them to the host. This uses up 20 ring entries, allowing us to supply only 20 packet buffers to the host with a 256 entry ring. This is a huge overhead when receiving small packets, and is most keenly felt when receiving MTU sized packets from off-host. The VIRTIO_NET_F_MRG_RXBUF feature flag is set by hosts which support using receive buffers which are smaller than the maximum packet size. In order to transfer large packets to the guest, the host merges together multiple receive buffers to form a larger logical buffer. The number of merged buffers is returned to the guest via a field in the virtio_net_hdr. Make use of this support by supplying single page receive buffers to the host. On receive, we extract the virtio_net_hdr, copy 128 bytes of the payload to the skb's linear data buffer and adjust the fragment offset to point to the remaining data. This ensures proper alignment and allows us to not use any paged data for small packets. If the payload occupies multiple pages, we simply append those pages as fragments and free the associated skbs. This scheme allows us to be efficient in our use of ring entries while still supporting large packets. Benchmarking using netperf from an external machine to a guest over a 10Gb/s network shows a 100% improvement from ~1Gb/s to ~2Gb/s. With a local host->guest benchmark with GSO disabled on the host side, throughput was seen to increase from 700Mb/s to 1.7Gb/s. Based on a patch from Herbert Xu. Signed-off-by: Mark McLoughlin <markmc@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv) Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/virtio_net.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 5e33761b9b8a..5cdd0aa8bde9 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -20,6 +20,7 @@
#define VIRTIO_NET_F_HOST_TSO6 12 /* Host can handle TSOv6 in. */
#define VIRTIO_NET_F_HOST_ECN 13 /* Host can handle TSO[6] w/ ECN in. */
#define VIRTIO_NET_F_HOST_UFO 14 /* Host can handle UFO in. */
+#define VIRTIO_NET_F_MRG_RXBUF 15 /* Host can merge receive buffers. */
struct virtio_net_config
{
@@ -44,4 +45,12 @@ struct virtio_net_hdr
__u16 csum_start; /* Position to start checksumming from */
__u16 csum_offset; /* Offset after that to place checksum */
};
+
+/* This is the version of the header to use when the MRG_RXBUF
+ * feature has been negotiated. */
+struct virtio_net_hdr_mrg_rxbuf {
+ struct virtio_net_hdr hdr;
+ __u16 num_buffers; /* Number of merged rx buffers */
+};
+
#endif /* _LINUX_VIRTIO_NET_H */