From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:43509) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TGJ9m-0003XI-3R for qemu-devel@nongnu.org; Mon, 24 Sep 2012 20:37:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TGJ9k-0004Wk-TC for qemu-devel@nongnu.org; Mon, 24 Sep 2012 20:37:46 -0400 Received: from mail-oa0-f45.google.com ([209.85.219.45]:54665) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TGJ9k-0004Wa-MY for qemu-devel@nongnu.org; Mon, 24 Sep 2012 20:37:44 -0400 Received: by oagi18 with SMTP id i18so1340245oag.4 for ; Mon, 24 Sep 2012 17:37:44 -0700 (PDT) From: Anthony Liguori In-Reply-To: <04d3e68d5be34a87514a33fcd789339748d43cb5.1348527749.git.mst@redhat.com> References: <04d3e68d5be34a87514a33fcd789339748d43cb5.1348527749.git.mst@redhat.com> Date: Mon, 24 Sep 2012 19:37:40 -0500 Message-ID: <87a9wf0wff.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [Qemu-devel] [PATCH 04/14] virtio-net: avoid sg copy List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" , qemu-devel@nongnu.org, Jason Wang , stefanha@linux.vnet.ibm.com, aurelien@aurel32.net "Michael S. Tsirkin" writes: > Avoid tweaking iovec during receive. This removes > the need to copy the vector. > Note: we already have an evil cast in work_around_broken_dhclient > and unfortunately this adds another one. > const on buf is ignored by this function anyway so arguably > this is not making things much worse. > > Signed-off-by: Michael S. Tsirkin > --- > hw/virtio-net.c | 45 +++++++++++++++++++++------------------------ > iov.h | 8 ++++---- > 2 files changed, 25 insertions(+), 28 deletions(-) > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c > index 0c5081e..6e53858 100644 > --- a/hw/virtio-net.c > +++ b/hw/virtio-net.c > @@ -503,7 +503,7 @@ static int virtio_net_has_buffers(VirtIONet *n, int bufsize) > * we should provide a mechanism to disable it to avoid polluting the host > * cache. > */ > -static void work_around_broken_dhclient(struct virtio_net_hdr *hdr, > +static void work_around_broken_dhclient(const struct virtio_net_hdr *hdr, > const uint8_t *buf, size_t size) > { > if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /* missing csum */ > @@ -513,31 +513,27 @@ static void work_around_broken_dhclient(struct virtio_net_hdr *hdr, > (buf[34] == 0 && buf[35] == 67)) { /* udp.srcport == bootps */ > /* FIXME this cast is evil */ > net_checksum_calculate((uint8_t *)buf, size); > - hdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM; > + ((struct virtio_net_hdr *)hdr)->flags &= > ~VIRTIO_NET_HDR_F_NEEDS_CSUM; > } > } > > -static int receive_header(VirtIONet *n, struct iovec *iov, int iovcnt, > - const void *buf, size_t size, size_t hdr_len) > +static int receive_header(VirtIONet *n, const struct iovec *iov, int iov_cnt, > + const void *buf, size_t size) > { > - struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)iov[0].iov_base; > int offset = 0; > > - hdr->flags = 0; > - hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE; > - > if (n->has_vnet_hdr) { > - memcpy(hdr, buf, sizeof(*hdr)); > - offset = sizeof(*hdr); > - work_around_broken_dhclient(hdr, buf + offset, size - offset); > + work_around_broken_dhclient(buf, buf + offset, size - > offset); I think it would be less ugly to cast here. > + offset = sizeof(struct virtio_net_hdr); > + iov_from_buf(iov, iov_cnt, 0, buf, offset); > + } else { > + struct virtio_net_hdr hdr = { > + .flags = 0, > + .gso_type = VIRTIO_NET_HDR_GSO_NONE > + }; > + iov_from_buf(iov, iov_cnt, 0, &hdr, sizeof hdr); > } > > - /* We only ever receive a struct virtio_net_hdr from the tapfd, > - * but we may be passing along a larger header to the guest. > - */ > - iov[0].iov_base += hdr_len; > - iov[0].iov_len -= hdr_len; > - > return offset; > } > > @@ -598,7 +594,8 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t > { > VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque; > struct virtio_net_hdr_mrg_rxbuf *mhdr = NULL; > - size_t offset, i; > + const struct iovec *sg = elem.in_sg; > + size_t offset, i, guest_offset; > > if (!virtio_net_can_receive(&n->nic->nc)) > return -1; > @@ -615,7 +612,7 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t > while (offset < size) { > VirtQueueElement elem; > int len, total; > - struct iovec sg[VIRTQUEUE_MAX_SIZE]; > + const struct iovec *sg = elem.in_sg; > > total = 0; > > @@ -640,20 +637,20 @@ static ssize_t virtio_net_receive(NetClientState *nc, const uint8_t *buf, size_t > exit(1); > } > > - memcpy(&sg, &elem.in_sg[0], sizeof(sg[0]) * elem.in_num); > - > if (i == 0) { > if (n->mergeable_rx_bufs) > mhdr = (struct virtio_net_hdr_mrg_rxbuf *)sg[0].iov_base; > > offset += receive_header(n, sg, elem.in_num, > - buf + offset, size - offset, > - n->guest_hdr_len); > + buf + offset, size - offset); > total += n->guest_hdr_len; > + guest_offset = n->guest_hdr_len; > + } else { > + guest_offset = 0; > } > > /* copy in packet. ugh */ > - len = iov_from_buf(sg, elem.in_num, 0, > + len = iov_from_buf(sg, elem.in_num, guest_offset, > buf + offset, size - offset); > total += len; > offset += len; > diff --git a/iov.h b/iov.h > index f0daefa..6c9fdf1 100644 > --- a/iov.h > +++ b/iov.h > @@ -90,8 +90,8 @@ void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt, > /* > * Partial copy of vector from iov to dst_iov (data is not copied). > * dst_iov overlaps iov at a specified offset. > - * size of dst_iov is at most bytes. Actual size is returned. > + * size of dst_iov is at most bytes. dst vector count is returned. > */ > -size_t iov_cpy(struct iovec *dst_iov, unsigned int dst_iov_cnt, > - const struct iovec *iov, unsigned int iov_cnt, > - size_t offset, size_t bytes); > +unsigned iov_cpy(struct iovec *dst_iov, unsigned int dst_iov_cnt, > + const struct iovec *iov, unsigned int iov_cnt, > + size_t offset, size_t bytes); I think this belongs in an earlier patch. Regards, Anthony Liguori > -- > MST