From e0953c8b85baaa38d77ebd5dc4051bc3837c1191 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 13 May 2012 15:34:20 +0300 Subject: [PATCH] tun: experimental zero copy tx support Let vhost-net utilize zero copy tx when used with tun. Signed-off-by: Michael S. Tsirkin --- drivers/net/tun.c | 132 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 127 insertions(+), 5 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index fe5cd2f30aba..c4459e02d609 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 */ @@ -602,8 +604,86 @@ 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, +static ssize_t tun_get_user(struct tun_struct *tun, void *msg_control, const struct iovec *iv, size_t count, int noblock) { @@ -612,6 +692,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, size_t len = count, 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) @@ -645,14 +728,46 @@ static ssize_t tun_get_user(struct tun_struct *tun, return -EINVAL; } - 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; @@ -726,6 +841,12 @@ 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++; @@ -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), file->f_flags & O_NONBLOCK); tun_put(tun); @@ -960,7 +1081,7 @@ 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, + return tun_get_user(tun, m->msg_control, m->msg_iov, total_len, m->msg_flags & MSG_DONTWAIT); } @@ -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; -- 2.39.5