Michael Dalton <mwdalton@xxxxxxxxxx> writes:
> The virtio_net driver's mergeable receive buffer allocator
> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> is > 4KB but only ~1500 bytes of the buffer is used to store
> packet data, reducing the effective TCP window size
> substantially. This patch addresses the performance concerns
> with mergeable receive buffers by allocating MTU-sized packet
> buffers using page frag allocators. If more than MAX_SKB_FRAGS
> buffers are needed, the SKB frag_list is used.
>
> Signed-off-by: Michael Dalton <mwdalton@xxxxxxxxxx>
Hi Michael,
Nice work! Just one comment. Your patch highlights the
anachronistic name MAX_PACKET_LEN: it was from the original
implementation which only supported 1500 byte packets, and only used in
one place.
Please apply a first patch like this, then come up with a new constant
name (GOOD_PACKET_LEN?) for that value. Because it's not the maximum
packet we can receive for mergable buffers.
Thanks,
Rusty.
Subject: virtio_net: remove anachronistic MAX_PACKET_LEN constant.
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
The initial implementation of virtio_net only allowed ethernet-style
MTU packets; with more recent features this isn't true. Move the
constant into the function where it's used.
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 057ea13..dcbfccd 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -35,8 +35,6 @@ static bool csum = true, gso = true;
module_param(csum, bool, 0444);
module_param(gso, bool, 0444);
-/* FIXME: MTU in config. */
-#define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
#define GOOD_COPY_LEN 128
#define VIRTNET_DRIVER_VERSION "1.0.0"
@@ -434,12 +432,13 @@ static int add_recvbuf_small(struct receive_queue *rq, gfp_t gfp)
struct sk_buff *skb;
struct skb_vnet_hdr *hdr;
int err;
+ const int len = ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN;
- skb = __netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN, gfp);
+ skb = __netdev_alloc_skb_ip_align(vi->dev, len, gfp);
if (unlikely(!skb))
return -ENOMEM;
- skb_put(skb, MAX_PACKET_LEN);
+ skb_put(skb, len);
hdr = skb_vnet_hdr(skb);
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
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