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Date: Mon, 04 Jun 2012 12:48:17 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: eric.dumazet@...il.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
davem@...emloft.net, Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: [PATCHv3 6/6] tun: experimental zero copy tx support
On 05/13/2012 08:34 PM, Michael S. Tsirkin wrote:
> Let vhost-net utilize zero copy tx when used with tun.
>
> Signed-off-by: Michael S. Tsirkin<mst@...hat.com>
> ---
> drivers/net/tun.c | 146 +++++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 134 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index fe5cd2f3..74d7e5e 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -100,6 +100,8 @@ do { \
> } while (0)
> #endif
>
> +#define GOODCOPY_LEN 128
> +
> #define FLT_EXACT_COUNT 8
> struct tap_filter {
> unsigned int count; /* Number of addrs. Zero means disabled */
> @@ -602,19 +604,100 @@ static struct sk_buff *tun_alloc_skb(struct tun_struct *tun,
> return skb;
> }
>
> +/* set skb frags from iovec, this can move to core network code for reuse */
> +static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
> + int offset, size_t count)
> +{
> + int len = iov_length(from, count) - offset;
> + int copy = skb_headlen(skb);
> + int size, offset1 = 0;
> + int i = 0;
> +
> + /* Skip over from offset */
> + while (count&& (offset>= from->iov_len)) {
> + offset -= from->iov_len;
> + ++from;
> + --count;
> + }
> +
> + /* copy up to skb headlen */
> + while (count&& (copy> 0)) {
> + size = min_t(unsigned int, copy, from->iov_len - offset);
> + if (copy_from_user(skb->data + offset1, from->iov_base + offset,
> + size))
> + return -EFAULT;
> + if (copy> size) {
> + ++from;
> + --count;
> + offset = 0;
> + } else
> + offset += size;
> + copy -= size;
> + offset1 += size;
> + }
> +
> + if (len == offset1)
> + return 0;
> +
> + while (count--) {
> + struct page *page[MAX_SKB_FRAGS];
> + int num_pages;
> + unsigned long base;
> + unsigned long truesize;
> +
> + len = from->iov_len - offset;
> + if (!len) {
> + offset = 0;
> + ++from;
> + continue;
> + }
> + base = (unsigned long)from->iov_base + offset;
> + size = ((base& ~PAGE_MASK) + len + ~PAGE_MASK)>> PAGE_SHIFT;
> + if (i + size> MAX_SKB_FRAGS)
> + return -EMSGSIZE;
> + num_pages = get_user_pages_fast(base, size, 0,&page[i]);
> + if (num_pages != size) {
> + for (i = 0; i< num_pages; i++)
> + put_page(page[i]);
> + return -EFAULT;
> + }
> + truesize = size * PAGE_SIZE;
> + skb->data_len += len;
> + skb->len += len;
> + skb->truesize += truesize;
> + atomic_add(truesize,&skb->sk->sk_wmem_alloc);
> + while (len) {
> + int off = base& ~PAGE_MASK;
> + int size = min_t(int, len, PAGE_SIZE - off);
> + __skb_fill_page_desc(skb, i, page[i], off, size);
> + skb_shinfo(skb)->nr_frags++;
> + /* increase sk_wmem_alloc */
> + base += size;
> + len -= size;
> + i++;
> + }
> + offset = 0;
> + ++from;
> + }
> + return 0;
> +}
> +
> /* Get packet from user space buffer */
> -static ssize_t tun_get_user(struct tun_struct *tun,
> - const struct iovec *iv, size_t count,
> - int noblock)
> +static ssize_t tun_get_user(struct tun_struct *tun, void *msg_control,
> + const struct iovec *iv, size_t total_len,
> + size_t count, int noblock)
> {
Looks like V2 uses count as the number of vectors and V3 correct this,
so does V3 still have any issue during test?
> struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
> struct sk_buff *skb;
> - size_t len = count, align = NET_SKB_PAD;
> + size_t len = total_len, align = NET_SKB_PAD;
> struct virtio_net_hdr gso = { 0 };
> int offset = 0;
> + int copylen;
> + bool zerocopy = false;
> + int err;
>
> if (!(tun->flags& TUN_NO_PI)) {
> - if ((len -= sizeof(pi))> count)
> + if ((len -= sizeof(pi))> total_len)
> return -EINVAL;
>
> if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
> @@ -623,7 +706,7 @@ static ssize_t tun_get_user(struct tun_struct *tun,
> }
>
> if (tun->flags& TUN_VNET_HDR) {
> - if ((len -= tun->vnet_hdr_sz)> count)
> + if ((len -= tun->vnet_hdr_sz)> total_len)
> return -EINVAL;
>
> if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
> @@ -645,14 +728,46 @@ static ssize_t tun_get_user(struct tun_struct *tun,
> return -EINVAL;
> }
>
Add a check of UIO_MAXIOV like macvtap? Other looks good to me.
Thanks.
> - skb = tun_alloc_skb(tun, align, len, gso.hdr_len, noblock);
> + if (msg_control)
> + zerocopy = true;
> +
> + if (zerocopy) {
> + /* Userspace may produce vectors with count greater than
> + * MAX_SKB_FRAGS, so we need to linearize parts of the skb
> + * to let the rest of data to be fit in the frags.
> + */
> + if (count> MAX_SKB_FRAGS) {
> + copylen = iov_length(iv, count - MAX_SKB_FRAGS);
> + if (copylen< offset)
> + copylen = 0;
> + else
> + copylen -= offset;
> + } else
> + copylen = 0;
> + /* There are 256 bytes to be copied in skb, so there is enough
> + * room for skb expand head in case it is used.
> + * The rest of the buffer is mapped from userspace.
> + */
> + if (copylen< gso.hdr_len)
> + copylen = gso.hdr_len;
> + if (!copylen)
> + copylen = GOODCOPY_LEN;
> + } else
> + copylen = len;
> +
> + skb = tun_alloc_skb(tun, align, copylen, gso.hdr_len, noblock);
> if (IS_ERR(skb)) {
> if (PTR_ERR(skb) != -EAGAIN)
> tun->dev->stats.rx_dropped++;
> return PTR_ERR(skb);
> }
>
> - if (skb_copy_datagram_from_iovec(skb, 0, iv, offset, len)) {
> + if (zerocopy)
> + err = zerocopy_sg_from_iovec(skb, iv, offset, count);
> + else
> + err = skb_copy_datagram_from_iovec(skb, 0, iv, offset, len);
> +
> + if (err) {
> tun->dev->stats.rx_dropped++;
> kfree_skb(skb);
> return -EFAULT;
> @@ -726,12 +841,18 @@ static ssize_t tun_get_user(struct tun_struct *tun,
> skb_shinfo(skb)->gso_segs = 0;
> }
>
> + /* copy skb_ubuf_info for callback when skb has no error */
> + if (zerocopy) {
> + skb_shinfo(skb)->destructor_arg = msg_control;
> + skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> + }
> +
> netif_rx_ni(skb);
>
> tun->dev->stats.rx_packets++;
> tun->dev->stats.rx_bytes += len;
>
> - return count;
> + return total_len;
> }
>
> static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
> @@ -746,7 +867,7 @@ static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
>
> tun_debug(KERN_INFO, tun, "tun_chr_write %ld\n", count);
>
> - result = tun_get_user(tun, iv, iov_length(iv, count),
> + result = tun_get_user(tun, NULL, iv, iov_length(iv, count), count,
> file->f_flags& O_NONBLOCK);
>
> tun_put(tun);
> @@ -960,8 +1081,8 @@ static int tun_sendmsg(struct kiocb *iocb, struct socket *sock,
> struct msghdr *m, size_t total_len)
> {
> struct tun_struct *tun = container_of(sock, struct tun_struct, socket);
> - return tun_get_user(tun, m->msg_iov, total_len,
> - m->msg_flags& MSG_DONTWAIT);
> + return tun_get_user(tun, m->msg_control, m->msg_iov, total_len,
> + m->msg_iovlen, m->msg_flags& MSG_DONTWAIT);
> }
>
> static int tun_recvmsg(struct kiocb *iocb, struct socket *sock,
> @@ -1130,6 +1251,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
> sock_init_data(&tun->socket, sk);
> sk->sk_write_space = tun_sock_write_space;
> sk->sk_sndbuf = INT_MAX;
> + sock_set_flag(sk, SOCK_ZEROCOPY);
>
> tun_sk(sk)->tun = tun;
>
--
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