linux-kernel - [PATCH] virtio_net: enable big packets for large MTU values

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Date:   Wed, 29 Mar 2017 15:38:09 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: [PATCH] virtio_net: enable big packets for large MTU values

If one enables e.g. jumbo frames without mergeable
buffers, packets won't fit in 1500 byte buffers
we use. Switch to big packet mode instead.
TODO: make sizing more exact, possibly extend small
packet mode to use larger pages.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/net/virtio_net.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e0fb3707..9dc31dc 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2428,6 +2428,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 			dev->mtu = mtu;
 			dev->max_mtu = mtu;
 		}
+
+		/* TODO: size buffers correctly in this case. */
+		if (dev->mtu > ETH_DATA_LEN)
+			vi->big_packets = true;
 	}
 
 	if (vi->any_header_sg)
-- 
MST