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Re: [Qemu-devel] [PATCH 04/14] virtio-net: avoid sg copy
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH 04/14] virtio-net: avoid sg copy |
Date: |
Mon, 24 Sep 2012 19:37:40 -0500 |
User-agent: |
Notmuch/0.13.2+93~ged93d79 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
"Michael S. Tsirkin" <address@hidden> 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 <address@hidden>
> ---
> 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
- [Qemu-devel] [PATCH 00/14] virtio-net: iovec handling cleanup, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 01/14] virtio-net: track host/guest header length, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 03/14] iov: add iov_cpy, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 04/14] virtio-net: avoid sg copy, Michael S. Tsirkin, 2012/09/24
- Re: [Qemu-devel] [PATCH 04/14] virtio-net: avoid sg copy,
Anthony Liguori <=
- [Qemu-devel] [PATCH 05/14] virtio-net: use safe iov operations for rx, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 07/14] virtio-net: first s/g is always at start of buf, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 02/14] iov: add const annotation, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 08/14] virtio-net: switch tx to safe iov functions, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 09/14] virtio-net: simplify rx code, Michael S. Tsirkin, 2012/09/24
- [Qemu-devel] [PATCH 06/14] virtio-net: refactor receive_hdr, Michael S. Tsirkin, 2012/09/24