在 2021/4/2 下午9:26, Eric Dumazet 写道:
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize
under-estimation for tiny skbs") brought a ~10% performance drop.
The reason for the performance drop was that GRO was forced
to chain sk_buff (using skb_shinfo(skb)->frag_list), which
uses more memory but also cause packet consumers to go over
a lot of overhead handling all the tiny skbs.
It turns out that virtio_net page_to_skb() has a wrong strategy :
It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then
copies 128 bytes from the page, before feeding the packet to GRO stack.
This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize
under-estimation for tiny skbs") because GRO was using 2 frags per MSS,
meaning we were not packing MSS with 100% efficiency.
Fix is to pull only the ethernet header in page_to_skb()
Then, we change virtio_net_hdr_to_skb() to pull the missing
headers, instead of assuming they were already pulled by callers.
This fixes the performance regression, but could also allow virtio_net
to accept packets with more than 128bytes of headers.
Many thanks to Xuan Zhuo for his report, and his tests/help.
Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs")
Reported-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Link: https://www.spinics.net/lists/netdev/msg731397.html
Co-Developed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
---
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
drivers/net/virtio_net.c | 10 +++++++---
include/linux/virtio_net.h | 14 +++++++++-----
2 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 82e520d2cb1229a0c7b9fd0def3e4a7135536478..0824e6999e49957f7aaf7c990f6259792d42f32b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -406,9 +406,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
offset += hdr_padded_len;
p += hdr_padded_len;
- copy = len;
- if (copy > skb_tailroom(skb))
- copy = skb_tailroom(skb);
+ /* Copy all frame if it fits skb->head, otherwise
+ * we let virtio_net_hdr_to_skb() and GRO pull headers as needed.
+ */
+ if (len <= skb_tailroom(skb))
+ copy = len;
+ else
+ copy = ETH_HLEN + metasize;
skb_put_data(skb, p, copy);
if (metasize) {
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 98775d7fa69632e2c2da30b581a666f7fbb94b64..b465f8f3e554f27ced45c35f54f113cf6dce1f07 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -65,14 +65,18 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
skb_reset_mac_header(skb);
if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
- u16 start = __virtio16_to_cpu(little_endian, hdr->csum_start);
- u16 off = __virtio16_to_cpu(little_endian, hdr->csum_offset);
+ u32 start = __virtio16_to_cpu(little_endian, hdr->csum_start);
+ u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset);
+ u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16));
+
+ if (!pskb_may_pull(skb, needed))
+ return -EINVAL;
if (!skb_partial_csum_set(skb, start, off))
return -EINVAL;
p_off = skb_transport_offset(skb) + thlen;
- if (p_off > skb_headlen(skb))
+ if (!pskb_may_pull(skb, p_off))
return -EINVAL;
} else {
/* gso packets without NEEDS_CSUM do not set transport_offset.
@@ -102,14 +106,14 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
}
p_off = keys.control.thoff + thlen;
- if (p_off > skb_headlen(skb) ||
+ if (!pskb_may_pull(skb, p_off) ||
keys.basic.ip_proto != ip_proto)
return -EINVAL;
skb_set_transport_header(skb, keys.control.thoff);
} else if (gso_type) {
p_off = thlen;
- if (p_off > skb_headlen(skb))
+ if (!pskb_may_pull(skb, p_off))
return -EINVAL;
}
}
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