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Re: [Qemu-devel] [RFC PATCH] vring: calculate descriptor address directl
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC PATCH] vring: calculate descriptor address directly |
Date: |
Thu, 27 Nov 2014 17:49:02 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
On 27/11/2014 11:15, Peter Lieven wrote:
> vring_map causes a huge overhead by calling memory_region_find everytime.
> the vring_map is executed already on vring_setup and there is also the memory
> region referenced.
>
> Signed-off-by: Peter Lieven <address@hidden>
vring_map/unmap is going to disappear and be replaced by
address_space_map/unmap, so for now I'd rather keep it...
Paolo
> ---
> hw/virtio/dataplane/vring.c | 51
> +++++--------------------------------------
> 1 file changed, 5 insertions(+), 46 deletions(-)
>
> diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c
> index 61f6d83..cfd484f 100644
> --- a/hw/virtio/dataplane/vring.c
> +++ b/hw/virtio/dataplane/vring.c
> @@ -53,15 +53,6 @@ out:
> return NULL;
> }
>
> -static void vring_unmap(void *buffer, bool is_write)
> -{
> - ram_addr_t addr;
> - MemoryRegion *mr;
> -
> - mr = qemu_ram_addr_from_host(buffer, &addr);
> - memory_region_unref(mr);
> -}
> -
> /* Map the guest's vring to host memory */
> bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
> {
> @@ -160,7 +151,6 @@ static int get_desc(Vring *vring, VirtQueueElement *elem,
> unsigned *num;
> struct iovec *iov;
> hwaddr *addr;
> - MemoryRegion *mr;
>
> if (desc->flags & VRING_DESC_F_WRITE) {
> num = &elem->in_num;
> @@ -186,13 +176,10 @@ static int get_desc(Vring *vring, VirtQueueElement
> *elem,
> }
>
> /* TODO handle non-contiguous memory across region boundaries */
> - iov->iov_base = vring_map(&mr, desc->addr, desc->len,
> - desc->flags & VRING_DESC_F_WRITE);
> - if (!iov->iov_base) {
> - error_report("Failed to map descriptor addr %#" PRIx64 " len %u",
> - (uint64_t)desc->addr, desc->len);
> + if (desc->addr + desc->len > memory_region_size(vring->mr)) {
> return -EFAULT;
> }
> + iov->iov_base = (void*) memory_region_get_ram_ptr(vring->mr) +
> desc->addr;
>
> /* The MemoryRegion is looked up again and unref'ed later, leave the
> * ref in place. */
> @@ -230,22 +217,14 @@ static int get_indirect(Vring *vring, VirtQueueElement
> *elem,
>
> do {
> struct vring_desc *desc_ptr;
> - MemoryRegion *mr;
>
> /* Translate indirect descriptor */
> - desc_ptr = vring_map(&mr,
> - indirect->addr + found * sizeof(desc),
> - sizeof(desc), false);
> - if (!desc_ptr) {
> - error_report("Failed to map indirect descriptor "
> - "addr %#" PRIx64 " len %zu",
> - (uint64_t)indirect->addr + found * sizeof(desc),
> - sizeof(desc));
> - vring->broken = true;
> + if (indirect->addr + (found + 1) * sizeof(desc) >
> memory_region_size(vring->mr)) {
> return -EFAULT;
> }
> + desc_ptr = (void*) memory_region_get_ram_ptr(vring->mr) +
> + indirect->addr + found * sizeof(desc);
> desc = *desc_ptr;
> - memory_region_unref(mr);
>
> /* Ensure descriptor has been loaded before accessing fields */
> barrier(); /* read_barrier_depends(); */
> @@ -273,23 +252,6 @@ static int get_indirect(Vring *vring, VirtQueueElement
> *elem,
> return 0;
> }
>
> -static void vring_unmap_element(VirtQueueElement *elem)
> -{
> - int i;
> -
> - /* This assumes that the iovecs, if changed, are never moved past
> - * the end of the valid area. This is true if iovec manipulations
> - * are done with iov_discard_front and iov_discard_back.
> - */
> - for (i = 0; i < elem->out_num; i++) {
> - vring_unmap(elem->out_sg[i].iov_base, false);
> - }
> -
> - for (i = 0; i < elem->in_num; i++) {
> - vring_unmap(elem->in_sg[i].iov_base, true);
> - }
> -}
> -
> /* This looks in the virtqueue and for the first available buffer, and
> converts
> * it to an iovec for convenient access. Since descriptors consist of some
> * number of output then some number of input descriptors, it's actually two
> @@ -399,7 +361,6 @@ out:
> if (ret == -EFAULT) {
> vring->broken = true;
> }
> - vring_unmap_element(elem);
> return ret;
> }
>
> @@ -413,8 +374,6 @@ void vring_push(Vring *vring, VirtQueueElement *elem, int
> len)
> unsigned int head = elem->index;
> uint16_t new;
>
> - vring_unmap_element(elem);
> -
> /* Don't touch vring if a fatal error occurred */
> if (vring->broken) {
> return;
>