Commit 3b3b0628 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Michael S. Tsirkin
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virtio: slim down allocation of VirtQueueElements 



Build the addresses and s/g lists on the stack, and then copy them
to a VirtQueueElement that is just as big as required to contain this
particular s/g list.  The cost of the copy is minimal compared to that
of a large malloc.

When virtqueue_map is used on the destination side of migration or on
loadvm, the iovecs have already been split at memory region boundary,
so we can just reuse the out_num/in_num we find in the file.

Reviewed-by: default avatarCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 3724650d

hw/virtio/virtio.c

+51 −31
Original line number Diff line number Diff line
@@ -448,6 +448,32 @@ int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, 
    return in_bytes <= in_total && out_bytes <= out_total;

}



static void virtqueue_map_desc(unsigned int *p_num_sg, hwaddr *addr, struct iovec *iov,

                               unsigned int max_num_sg, bool is_write,

                               hwaddr pa, size_t sz)

{

    unsigned num_sg = *p_num_sg;

    assert(num_sg <= max_num_sg);



    while (sz) {

        hwaddr len = sz;



        if (num_sg == max_num_sg) {

            error_report("virtio: too many write descriptors in indirect table");

            exit(1);

        }



        iov[num_sg].iov_base = cpu_physical_memory_map(pa, &len, is_write);

        iov[num_sg].iov_len = len;

        addr[num_sg] = pa;



        sz -= len;

        pa += len;

        num_sg++;

    }

    *p_num_sg = num_sg;

}



static void virtqueue_map_iovec(struct iovec *sg, hwaddr *addr,

                                unsigned int *num_sg, unsigned int max_size,

                                int is_write)
@@ -474,20 +500,10 @@ static void virtqueue_map_iovec(struct iovec *sg, hwaddr *addr, 
            error_report("virtio: error trying to map MMIO memory");

            exit(1);

        }

        if (len == sg[i].iov_len) {

            continue;

        }

        if (*num_sg >= max_size) {

            error_report("virtio: memory split makes iovec too large");

        if (len != sg[i].iov_len) {

            error_report("virtio: unexpected memory split");

            exit(1);

        }

        memmove(sg + i + 1, sg + i, sizeof(*sg) * (*num_sg - i));

        memmove(addr + i + 1, addr + i, sizeof(*addr) * (*num_sg - i));

        assert(len < sg[i + 1].iov_len);

        sg[i].iov_len = len;

        addr[i + 1] += len;

        sg[i + 1].iov_len -= len;

        ++*num_sg;

    }

}
@@ -526,14 +542,16 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) 
    hwaddr desc_pa = vq->vring.desc;

    VirtIODevice *vdev = vq->vdev;

    VirtQueueElement *elem;

    unsigned out_num, in_num;

    hwaddr addr[VIRTQUEUE_MAX_SIZE];

    struct iovec iov[VIRTQUEUE_MAX_SIZE];



    if (!virtqueue_num_heads(vq, vq->last_avail_idx)) {

        return NULL;

    }



    /* When we start there are none of either input nor output. */

    elem = virtqueue_alloc_element(sz, VIRTQUEUE_MAX_SIZE, VIRTQUEUE_MAX_SIZE);

    elem->out_num = elem->in_num = 0;

    out_num = in_num = 0;



    max = vq->vring.num;
@@ -556,37 +574,39 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) 


    /* Collect all the descriptors */

    do {

        struct iovec *sg;

        hwaddr pa = vring_desc_addr(vdev, desc_pa, i);

        size_t len = vring_desc_len(vdev, desc_pa, i);



        if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE) {

            if (elem->in_num >= VIRTQUEUE_MAX_SIZE) {

                error_report("Too many write descriptors in indirect table");

                exit(1);

            }

            elem->in_addr[elem->in_num] = vring_desc_addr(vdev, desc_pa, i);

            sg = &elem->in_sg[elem->in_num++];

            virtqueue_map_desc(&in_num, addr + out_num, iov + out_num,

                               VIRTQUEUE_MAX_SIZE - out_num, true, pa, len);

        } else {

            if (elem->out_num >= VIRTQUEUE_MAX_SIZE) {

                error_report("Too many read descriptors in indirect table");

            if (in_num) {

                error_report("Incorrect order for descriptors");

                exit(1);

            }

            elem->out_addr[elem->out_num] = vring_desc_addr(vdev, desc_pa, i);

            sg = &elem->out_sg[elem->out_num++];

            virtqueue_map_desc(&out_num, addr, iov,

                               VIRTQUEUE_MAX_SIZE, false, pa, len);

        }



        sg->iov_len = vring_desc_len(vdev, desc_pa, i);



        /* If we've got too many, that implies a descriptor loop. */

        if ((elem->in_num + elem->out_num) > max) {

        if ((in_num + out_num) > max) {

            error_report("Looped descriptor");

            exit(1);

        }

    } while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max);



    /* Now map what we have collected */

    virtqueue_map(elem);



    /* Now copy what we have collected and mapped */

    elem = virtqueue_alloc_element(sz, out_num, in_num);

    elem->index = head;

    for (i = 0; i < out_num; i++) {

        elem->out_addr[i] = addr[i];

        elem->out_sg[i] = iov[i];

    }

    for (i = 0; i < in_num; i++) {

        elem->in_addr[i] = addr[out_num + i];

        elem->in_sg[i] = iov[out_num + i];

    }



    vq->inuse++;