From 5dba97ebdc92f1ac3c9ac27d8eac52ed2348fae1 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Sun, 31 Jan 2016 11:29:02 +0100 Subject: vring: 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. Reviewed-by: Cornelia Huck Signed-off-by: Paolo Bonzini Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- hw/virtio/dataplane/vring.c | 53 ++++++++++++++++++++++++++++++--------------- 1 file changed, 36 insertions(+), 17 deletions(-) diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c index 57ada3b..4308d9f 100644 --- a/hw/virtio/dataplane/vring.c +++ b/hw/virtio/dataplane/vring.c @@ -218,8 +218,14 @@ bool vring_should_notify(VirtIODevice *vdev, Vring *vring) new, old); } - -static int get_desc(Vring *vring, VirtQueueElement *elem, +typedef struct VirtQueueCurrentElement { + unsigned in_num; + unsigned out_num; + hwaddr addr[VIRTQUEUE_MAX_SIZE]; + struct iovec iov[VIRTQUEUE_MAX_SIZE]; +} VirtQueueCurrentElement; + +static int get_desc(Vring *vring, VirtQueueCurrentElement *elem, struct vring_desc *desc) { unsigned *num; @@ -230,12 +236,12 @@ static int get_desc(Vring *vring, VirtQueueElement *elem, if (desc->flags & VRING_DESC_F_WRITE) { num = &elem->in_num; - iov = &elem->in_sg[*num]; - addr = &elem->in_addr[*num]; + iov = &elem->iov[elem->out_num + *num]; + addr = &elem->addr[elem->out_num + *num]; } else { num = &elem->out_num; - iov = &elem->out_sg[*num]; - addr = &elem->out_addr[*num]; + iov = &elem->iov[*num]; + addr = &elem->addr[*num]; /* If it's an output descriptor, they're all supposed * to come before any input descriptors. */ @@ -299,7 +305,8 @@ static bool read_vring_desc(VirtIODevice *vdev, /* This is stolen from linux/drivers/vhost/vhost.c. */ static int get_indirect(VirtIODevice *vdev, Vring *vring, - VirtQueueElement *elem, struct vring_desc *indirect) + VirtQueueCurrentElement *cur_elem, + struct vring_desc *indirect) { struct vring_desc desc; unsigned int i = 0, count, found = 0; @@ -351,7 +358,7 @@ static int get_indirect(VirtIODevice *vdev, Vring *vring, return -EFAULT; } - ret = get_desc(vring, elem, &desc); + ret = get_desc(vring, cur_elem, &desc); if (ret < 0) { vring->broken |= (ret == -EFAULT); return ret; @@ -394,6 +401,7 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz) struct vring_desc desc; unsigned int i, head, found = 0, num = vring->vr.num; uint16_t avail_idx, last_avail_idx; + VirtQueueCurrentElement cur_elem; VirtQueueElement *elem = NULL; int ret; @@ -403,10 +411,7 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz) goto out; } - elem = virtqueue_alloc_element(sz, VIRTQUEUE_MAX_SIZE, VIRTQUEUE_MAX_SIZE); - - /* Initialize elem so it can be safely unmapped */ - elem->in_num = elem->out_num = 0; + cur_elem.in_num = cur_elem.out_num = 0; /* Check it isn't doing very strange things with descriptor numbers. */ last_avail_idx = vring->last_avail_idx; @@ -433,8 +438,6 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz) * the index we've seen. */ head = vring_get_avail_ring(vdev, vring, last_avail_idx % num); - elem->index = head; - /* If their number is silly, that's an error. */ if (unlikely(head >= num)) { error_report("Guest says index %u > %u is available", head, num); @@ -461,14 +464,14 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz) barrier(); if (desc.flags & VRING_DESC_F_INDIRECT) { - ret = get_indirect(vdev, vring, elem, &desc); + ret = get_indirect(vdev, vring, &cur_elem, &desc); if (ret < 0) { goto out; } continue; } - ret = get_desc(vring, elem, &desc); + ret = get_desc(vring, &cur_elem, &desc); if (ret < 0) { goto out; } @@ -483,6 +486,18 @@ void *vring_pop(VirtIODevice *vdev, Vring *vring, size_t sz) virtio_tswap16(vdev, vring->last_avail_idx); } + /* Now copy what we have collected and mapped */ + elem = virtqueue_alloc_element(sz, cur_elem.out_num, cur_elem.in_num); + elem->index = head; + for (i = 0; i < cur_elem.out_num; i++) { + elem->out_addr[i] = cur_elem.addr[i]; + elem->out_sg[i] = cur_elem.iov[i]; + } + for (i = 0; i < cur_elem.in_num; i++) { + elem->in_addr[i] = cur_elem.addr[cur_elem.out_num + i]; + elem->in_sg[i] = cur_elem.iov[cur_elem.out_num + i]; + } + return elem; out: @@ -490,7 +505,11 @@ out: if (ret == -EFAULT) { vring->broken = true; } - vring_unmap_element(elem); + + for (i = 0; i < cur_elem.out_num + cur_elem.in_num; i++) { + vring_unmap(cur_elem.iov[i].iov_base, false); + } + g_free(elem); return NULL; } -- cgit v1.1