From 3b3b0628217e2726069990ff9942a5d6d9816bd7 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Sun, 31 Jan 2016 11:29:01 +0100 Subject: [PATCH] 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: Cornelia Huck Signed-off-by: Paolo Bonzini Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- hw/virtio/virtio.c | 82 +++++++++++++++++++++++++++++++++--------------------- 1 file changed, 51 insertions(+), 31 deletions(-) diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 661a1e1536..c3e00a8124 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -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++; -- 2.11.4.GIT