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tap: use build_skb() for small packet

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We use tun_alloc_skb() which calls sock_alloc_send_pskb() to allocate
skb in the past. This socket based method is not suitable for high
speed userspace like virtualization which usually:

- ignore sk_sndbuf (INT_MAX) and expect to receive the packet as fast as
  possible
- don't want to be block at sendmsg()

To eliminate the above overheads, this patch tries to use build_skb()
for small packet. We will do this only when the following conditions
are all met:

- TAP instead of TUN
- sk_sndbuf is INT_MAX
- caller don't want to be blocked
- zerocopy is not used
- packet size is smaller enough to use build_skb()

Pktgen from guest to host shows ~11% improvement for rx pps of tap:

Before: ~1.70Mpps
After : ~1.88Mpps

What's more important, this makes it possible to implement XDP for tap
before creating skbs.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Wang 2017-08-11 19:41:16 +08:00 committed by David S. Miller
parent d0225784be
commit 66ccbc9c87
1 changed files with 91 additions and 21 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

70
drivers/net/tun.c
View file

@ -105,6 +105,8 @@ do { \
} while (0)
#endif
#define TUN_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)
/* TUN device flags */
/* IFF_ATTACH_QUEUE is never stored in device flags,
@ -170,6 +172,7 @@ struct tun_file {
struct list_head next;
struct tun_struct *detached;
struct skb_array tx_array;
struct page_frag alloc_frag;
};
struct tun_flow_entry {
@ -571,6 +574,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
}
if (tun)
skb_array_cleanup(&tfile->tx_array);
if (tfile->alloc_frag.page)
put_page(tfile->alloc_frag.page);
sock_put(&tfile->sk);
}
}
@ -1190,6 +1195,61 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
}
}
static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
int len, int noblock, bool zerocopy)
{
if ((tun->flags & TUN_TYPE_MASK) != IFF_TAP)
return false;
if (tfile->socket.sk->sk_sndbuf != INT_MAX)
return false;
if (!noblock)
return false;
if (zerocopy)
return false;
if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
return false;
return true;
}
static struct sk_buff *tun_build_skb(struct tun_file *tfile,
struct iov_iter *from,
int len)
{
struct page_frag *alloc_frag = &tfile->alloc_frag;
struct sk_buff *skb;
int buflen = SKB_DATA_ALIGN(len + TUN_RX_PAD) +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
char *buf;
size_t copied;
if (unlikely(!skb_page_frag_refill(buflen, alloc_frag, GFP_KERNEL)))
return ERR_PTR(-ENOMEM);
buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
copied = copy_page_from_iter(alloc_frag->page,
alloc_frag->offset + TUN_RX_PAD,
len, from);
if (copied != len)
return ERR_PTR(-EFAULT);
skb = build_skb(buf, buflen);
if (!skb)
return ERR_PTR(-ENOMEM);
skb_reserve(skb, TUN_RX_PAD);
skb_put(skb, len);
get_page(alloc_frag->page);
alloc_frag->offset += buflen;
return skb;
}
/* Get packet from user space buffer */
static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
void *msg_control, struct iov_iter *from,
@ -1263,6 +1323,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
zerocopy = true;
}
if (tun_can_build_skb(tun, tfile, len, noblock, zerocopy)) {
skb = tun_build_skb(tfile, from, len);
if (IS_ERR(skb)) {
this_cpu_inc(tun->pcpu_stats->rx_dropped);
return PTR_ERR(skb);
}
} else {
if (!zerocopy) {
copylen = len;
if (tun16_to_cpu(tun, gso.hdr_len) > good_linear)
@ -1288,6 +1355,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
kfree_skb(skb);
return -EFAULT;
}
}
if (virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun))) {
this_cpu_inc(tun->pcpu_stats->rx_frame_errors);
@ -2377,6 +2445,8 @@ static int tun_chr_open(struct inode *inode, struct file * file)
tfile->sk.sk_write_space = tun_sock_write_space;
tfile->sk.sk_sndbuf = INT_MAX;
tfile->alloc_frag.page = NULL;
file->private_data = tfile;
INIT_LIST_HEAD(&tfile->next);