Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753711Ab1EEVB1 (ORCPT ); Thu, 5 May 2011 17:01:27 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:40079 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753107Ab1EEVBZ (ORCPT ); Thu, 5 May 2011 17:01:25 -0400 Subject: Re: [PATCH V4 5/8]macvtap: macvtap TX zero-copy support From: Shirley Ma To: Sridhar Samudrala Cc: David Miller , mst@redhat.com, Eric Dumazet , Avi Kivity , Arnd Bergmann , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <4DC1DD83.2020801@us.ibm.com> References: <1304496893.20660.88.camel@localhost.localdomain> <4DC1DD83.2020801@us.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 05 May 2011 13:59:16 -0700 Message-ID: <1304629156.7076.61.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 (2.28.3-1.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8153 Lines: 252 On Wed, 2011-05-04 at 16:13 -0700, Sridhar Samudrala wrote: > On Wed, 2011-05-04 at 01:14 -0700, Shirley Ma wrote: > > Only when buffer size is greater than GOODCOPY_LEN (256), macvtap > > enables zero-copy. > > > > Signed-off-by: Shirley Ma > > --- > > > > drivers/net/macvtap.c | 126 ++++++++++++++++++++++++++++++++++++++++++++---- > > 1 files changed, 115 insertions(+), 11 deletions(-) > > > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > > index 6696e56..e8bc5ff 100644 > > --- a/drivers/net/macvtap.c > > +++ b/drivers/net/macvtap.c > > @@ -60,6 +60,7 @@ static struct proto macvtap_proto = { > > */ > > static dev_t macvtap_major; > > #define MACVTAP_NUM_DEVS 65536 > > +#define GOODCOPY_LEN 256 > > static struct class *macvtap_class; > > static struct cdev macvtap_cdev; > > > > @@ -340,6 +341,7 @@ static int macvtap_open(struct inode *inode, struct file *file) > > { > > struct net *net = current->nsproxy->net_ns; > > struct net_device *dev = dev_get_by_index(net, iminor(inode)); > > + struct macvlan_dev *vlan = netdev_priv(dev); > > struct macvtap_queue *q; > > int err; > > > > @@ -369,6 +371,16 @@ static int macvtap_open(struct inode *inode, struct file *file) > > q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP; > > q->vnet_hdr_sz = sizeof(struct virtio_net_hdr); > > > > + /* > > + * so far only VM uses macvtap, enable zero copy between guest > > + * kernel and host kernel when lower device supports high memory > > + * DMA > > + */ > Instead of VM uses macvtap, it makes it more clear to say 'KVM virtio > uses macvtap for guest networking'. > Also you are checking if lower device allows zerocopy, not high dma. Sure. > > > + if (vlan) { > > + if (vlan->lowerdev->features & NETIF_F_ZEROCOPY) > > + sock_set_flag(&q->sk, SOCK_ZEROCOPY); > > + } > > + > > Do we need to check for vlan? If required, both if conditions can be > combined. Yes, I will run more test before enabling it. > > err = macvtap_set_queue(dev, file, q); > > if (err) > > sock_put(&q->sk); > > @@ -433,6 +445,80 @@ static inline struct sk_buff *macvtap_alloc_skb(struct sock *sk, size_t prepad, > > 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; > > + skb_frag_t *f; > > + > > + /* Skip over from offset */ > > + while (offset >= from->iov_len) { > > + offset -= from->iov_len; > > + ++from; > > + --count; > > + } > > + > > + /* copy up to skb headlen */ > > + while (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; > > + } > > + copy -= size; > > + offset1 += size; > > + offset = 0; > > + } > > I think you need to check for count reaching zero in the above 2 while > loops. Doesn't hurt to check count here, in this case, caller has copylen/len/offset less than count/len already. > > + > > + if (len == offset1) > > + return 0; > > + > > + while (count--) { > > + struct page *page[MAX_SKB_FRAGS]; > > + int num_pages; > > + unsigned long base; > > + > > + len = from->iov_len - offset1; > > + if (!len) { > > + offset1 = 0; > > + ++from; > > + continue; > > + } > > + base = (unsigned long)from->iov_base + offset1; > > + size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT; > > + num_pages = get_user_pages_fast(base, size, 0, &page[i]); > > + if ((num_pages != size) || > > + (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)) > > + /* put_page is in skb free */ > > + return -EFAULT; > > + skb->data_len += len; > > + skb->len += len; > > + skb->truesize += len; > > + while (len) { > > + f = &skb_shinfo(skb)->frags[i]; > > + f->page = page[i]; > > + f->page_offset = base & ~PAGE_MASK; > > + f->size = min_t(int, len, PAGE_SIZE - f->page_offset); > > + skb_shinfo(skb)->nr_frags++; > > + /* increase sk_wmem_alloc */ > > + atomic_add(f->size, &skb->sk->sk_wmem_alloc); > > + base += f->size; > > + len -= f->size; > > + i++; > > + } > > + offset1 = 0; > > + ++from; > > + } > > + return 0; > > +} > > + > > /* > > * macvtap_skb_from_vnet_hdr and macvtap_skb_to_vnet_hdr should > > * be shared with the tun/tap driver. > > @@ -515,17 +601,19 @@ static int macvtap_skb_to_vnet_hdr(const struct sk_buff *skb, > > > > > > /* Get packet from user space buffer */ > > -static ssize_t macvtap_get_user(struct macvtap_queue *q, > > - const struct iovec *iv, size_t count, > > - int noblock) > > +static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m, > > + const struct iovec *iv, unsigned long total_len, > > + size_t count, int noblock) > > { > > struct sk_buff *skb; > > struct macvlan_dev *vlan; > > - size_t len = count; > > + unsigned long len = total_len; > > int err; > > struct virtio_net_hdr vnet_hdr = { 0 }; > > int vnet_hdr_len = 0; > > + int copylen, zerocopy; > zerocopy can be boolean Yes, I have changed it in V5. > > + zerocopy = sock_flag(&q->sk, SOCK_ZEROCOPY) && (len > GOODCOPY_LEN); > > if (q->flags & IFF_VNET_HDR) { > > vnet_hdr_len = q->vnet_hdr_sz; > > > > @@ -552,12 +640,28 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, > > if (unlikely(len < ETH_HLEN)) > > goto err; > > > > - skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, len, vnet_hdr.hdr_len, > > - noblock, &err); > > + if (zerocopy) > > + /* 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 buffer is mapped from userspace. > > + */ > > + copylen = GOODCOPY_LEN; > > + else > > + copylen = len; > > + > > + skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen, > > + vnet_hdr.hdr_len, noblock, &err); > > if (!skb) > > goto err; > > > > - err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len, len); > > + if (zerocopy) > > + err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count); > > + else > > + err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len, > > + len); > > + if (sock_flag(&q->sk, SOCK_ZEROCOPY)) > > + memcpy(&skb_shinfo(skb)->ubuf, m->msg_control, > > + sizeof(struct skb_ubuf_info)); > Why are you doing a separate check for this memcpy? Is this required > if the len < 256? Yes. But I have changed it V5 based on MST's suggestion to leave copied buffer maintain in vhost. > > if (err) > > goto err_kfree; > > > > @@ -579,7 +683,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, > > kfree_skb(skb); > > rcu_read_unlock_bh(); > > > > - return count; > > + return total_len; > > > > err_kfree: > > kfree_skb(skb); > > @@ -601,8 +705,8 @@ static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv, > > ssize_t result = -ENOLINK; > > struct macvtap_queue *q = file->private_data; > > > > - result = macvtap_get_user(q, iv, iov_length(iv, count), > > - file->f_flags & O_NONBLOCK); > > + result = macvtap_get_user(q, NULL, iv, iov_length(iv, count), count, > > + file->f_flags & O_NONBLOCK); > > return result; > > } > > > > @@ -815,7 +919,7 @@ static int macvtap_sendmsg(struct kiocb *iocb, struct socket *sock, > > struct msghdr *m, size_t total_len) > > { > > struct macvtap_queue *q = container_of(sock, struct macvtap_queue, sock); > > - return macvtap_get_user(q, m->msg_iov, total_len, > > + return macvtap_get_user(q, m, m->msg_iov, total_len, m->msg_iovlen, > > m->msg_flags & MSG_DONTWAIT); > > } > > > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/