Commit 4875bf14 authored by Vincenzo Maffione's avatar Vincenzo Maffione Committed by Jason Wang
Browse files

net: netmap: improve netmap_receive_iov() 



Changes:
  - Save CPU cycles by computing the return value while scanning the
    input iovec, rather than calling iov_size() at the end.
  - Remove check for s->tx != NULL, because it cannot happen.
  - Cache ring->tail in a local variable and use it to check for
    space in the TX ring. The use of nm_ring_empty() was invalid,
    because nobody is updating ring->cur and ring->head at that point.
  - In case we run out of netmap slots in the middle of a packet,
    move the wake-up point by advancing ring->cur, but do not
    expose the incomplete packet (i.e., by updating also ring->head).

Signed-off-by: default avatarVincenzo Maffione <v.maffione@gmail.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
parent c7cbb6b4

net/netmap.c

+17 −12
Original line number Diff line number Diff line
@@ -159,21 +159,22 @@ static ssize_t netmap_receive_iov(NetClientState *nc, 
{

    NetmapState *s = DO_UPCAST(NetmapState, nc, nc);

    struct netmap_ring *ring = s->tx;

    unsigned int tail = ring->tail;

    ssize_t totlen = 0;

    uint32_t last;

    uint32_t idx;

    uint8_t *dst;

    int j;

    uint32_t i;



    if (unlikely(!ring)) {

        /* Drop the packet. */

        return iov_size(iov, iovcnt);

    }



    last = i = ring->cur;

    last = i = ring->head;



    if (nm_ring_space(ring) < iovcnt) {

        /* Not enough netmap slots. */

        /* Not enough netmap slots. Tell the kernel that we have seen the new

         * available slots (so that it notifies us again when it has more

         * ones), but without publishing any new slots to be processed

         * (e.g., we don't advance ring->head). */

        ring->cur = tail;

        netmap_write_poll(s, true);

        return 0;

    }
@@ -183,14 +184,17 @@ static ssize_t netmap_receive_iov(NetClientState *nc, 
        int offset = 0;

        int nm_frag_size;



        totlen += iov_frag_size;



        /* Split each iovec fragment over more netmap slots, if

           necessary. */

        while (iov_frag_size) {

            nm_frag_size = MIN(iov_frag_size, ring->nr_buf_size);



            if (unlikely(nm_ring_empty(ring))) {

                /* We run out of netmap slots while splitting the

            if (unlikely(i == tail)) {

                /* We ran out of netmap slots while splitting the

                   iovec fragments. */

                ring->cur = tail;

                netmap_write_poll(s, true);

                return 0;

            }
@@ -212,12 +216,13 @@ static ssize_t netmap_receive_iov(NetClientState *nc, 
    /* The last slot must not have NS_MOREFRAG set. */

    ring->slot[last].flags &= ~NS_MOREFRAG;



    /* Now update ring->cur and ring->head. */

    ring->cur = ring->head = i;

    /* Now update ring->head and ring->cur to publish the new slots and

     * the new wakeup point. */

    ring->head = ring->cur = i;



    ioctl(s->nmd->fd, NIOCTXSYNC, NULL);



    return iov_size(iov, iovcnt);

    return totlen;

}



static ssize_t netmap_receive(NetClientState *nc,