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virtio: combine the read of a descriptor

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Compared to vring, virtio has a performance penalty of 10%.  Fix it
by combining all the reads for a descriptor in a single address_space_read
call.  This also simplifies the code nicely.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-01-31 11:29:03 +01:00 committed by Michael S. Tsirkin
parent 5dba97ebdc
commit aa570d6fb6
1 changed files with 35 additions and 51 deletions
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86
hw/virtio/virtio.c
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@ -107,35 +107,15 @@ void virtio_queue_update_rings(VirtIODevice *vdev, int n)
vring->align); vring->align);
} }
static inline uint64_t vring_desc_addr(VirtIODevice *vdev, hwaddr desc_pa, static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
int i) hwaddr desc_pa, int i)
{ {
hwaddr pa; address_space_read(&address_space_memory, desc_pa + i * sizeof(VRingDesc),
pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, addr); MEMTXATTRS_UNSPECIFIED, (void *)desc, sizeof(VRingDesc));
return virtio_ldq_phys(vdev, pa); virtio_tswap64s(vdev, &desc->addr);
} virtio_tswap32s(vdev, &desc->len);
virtio_tswap16s(vdev, &desc->flags);
static inline uint32_t vring_desc_len(VirtIODevice *vdev, hwaddr desc_pa, int i) virtio_tswap16s(vdev, &desc->next);
{
hwaddr pa;
pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, len);
return virtio_ldl_phys(vdev, pa);
}
static inline uint16_t vring_desc_flags(VirtIODevice *vdev, hwaddr desc_pa,
int i)
{
hwaddr pa;
pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, flags);
return virtio_lduw_phys(vdev, pa);
}
static inline uint16_t vring_desc_next(VirtIODevice *vdev, hwaddr desc_pa,
int i)
{
hwaddr pa;
pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, next);
return virtio_lduw_phys(vdev, pa);
} }
static inline uint16_t vring_avail_flags(VirtQueue *vq) static inline uint16_t vring_avail_flags(VirtQueue *vq)
@ -345,18 +325,18 @@ static unsigned int virtqueue_get_head(VirtQueue *vq, unsigned int idx)
return head; return head;
} }
static unsigned virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa, static unsigned virtqueue_read_next_desc(VirtIODevice *vdev, VRingDesc *desc,
unsigned int i, unsigned int max) hwaddr desc_pa, unsigned int max)
{ {
unsigned int next; unsigned int next;
/* If this descriptor says it doesn't chain, we're done. */ /* If this descriptor says it doesn't chain, we're done. */
if (!(vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_NEXT)) { if (!(desc->flags & VRING_DESC_F_NEXT)) {
return max; return max;
} }
/* Check they're not leading us off end of descriptors. */ /* Check they're not leading us off end of descriptors. */
next = vring_desc_next(vdev, desc_pa, i); next = desc->next;
/* Make sure compiler knows to grab that: we don't want it changing! */ /* Make sure compiler knows to grab that: we don't want it changing! */
smp_wmb(); smp_wmb();
@ -365,6 +345,7 @@ static unsigned virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa,
exit(1); exit(1);
} }
vring_desc_read(vdev, desc, desc_pa, next);
return next; return next;
} }
@ -381,6 +362,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
while (virtqueue_num_heads(vq, idx)) { while (virtqueue_num_heads(vq, idx)) {
VirtIODevice *vdev = vq->vdev; VirtIODevice *vdev = vq->vdev;
unsigned int max, num_bufs, indirect = 0; unsigned int max, num_bufs, indirect = 0;
VRingDesc desc;
hwaddr desc_pa; hwaddr desc_pa;
int i; int i;
@ -388,9 +370,10 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
num_bufs = total_bufs; num_bufs = total_bufs;
i = virtqueue_get_head(vq, idx++); i = virtqueue_get_head(vq, idx++);
desc_pa = vq->vring.desc; desc_pa = vq->vring.desc;
vring_desc_read(vdev, &desc, desc_pa, i);
if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) { if (desc.flags & VRING_DESC_F_INDIRECT) {
if (vring_desc_len(vdev, desc_pa, i) % sizeof(VRingDesc)) { if (desc.len % sizeof(VRingDesc)) {
error_report("Invalid size for indirect buffer table"); error_report("Invalid size for indirect buffer table");
exit(1); exit(1);
} }
@ -403,9 +386,10 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
/* loop over the indirect descriptor table */ /* loop over the indirect descriptor table */
indirect = 1; indirect = 1;
max = vring_desc_len(vdev, desc_pa, i) / sizeof(VRingDesc); max = desc.len / sizeof(VRingDesc);
desc_pa = vring_desc_addr(vdev, desc_pa, i); desc_pa = desc.addr;
num_bufs = i = 0; num_bufs = i = 0;
vring_desc_read(vdev, &desc, desc_pa, i);
} }
do { do {
@ -415,15 +399,15 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
exit(1); exit(1);
} }
if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE) { if (desc.flags & VRING_DESC_F_WRITE) {
in_total += vring_desc_len(vdev, desc_pa, i); in_total += desc.len;
} else { } else {
out_total += vring_desc_len(vdev, desc_pa, i); out_total += desc.len;
} }
if (in_total >= max_in_bytes && out_total >= max_out_bytes) { if (in_total >= max_in_bytes && out_total >= max_out_bytes) {
goto done; goto done;
} }
} while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max); } while ((i = virtqueue_read_next_desc(vdev, &desc, desc_pa, max)) != max);
if (!indirect) if (!indirect)
total_bufs = num_bufs; total_bufs = num_bufs;
@ -545,6 +529,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
unsigned out_num, in_num; unsigned out_num, in_num;
hwaddr addr[VIRTQUEUE_MAX_SIZE]; hwaddr addr[VIRTQUEUE_MAX_SIZE];
struct iovec iov[VIRTQUEUE_MAX_SIZE]; struct iovec iov[VIRTQUEUE_MAX_SIZE];
VRingDesc desc;
if (!virtqueue_num_heads(vq, vq->last_avail_idx)) { if (!virtqueue_num_heads(vq, vq->last_avail_idx)) {
return NULL; return NULL;
@ -560,33 +545,32 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
vring_set_avail_event(vq, vq->last_avail_idx); vring_set_avail_event(vq, vq->last_avail_idx);
} }
if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) { vring_desc_read(vdev, &desc, desc_pa, i);
if (vring_desc_len(vdev, desc_pa, i) % sizeof(VRingDesc)) { if (desc.flags & VRING_DESC_F_INDIRECT) {
if (desc.len % sizeof(VRingDesc)) {
error_report("Invalid size for indirect buffer table"); error_report("Invalid size for indirect buffer table");
exit(1); exit(1);
} }
/* loop over the indirect descriptor table */ /* loop over the indirect descriptor table */
max = vring_desc_len(vdev, desc_pa, i) / sizeof(VRingDesc); max = desc.len / sizeof(VRingDesc);
desc_pa = vring_desc_addr(vdev, desc_pa, i); desc_pa = desc.addr;
i = 0; i = 0;
vring_desc_read(vdev, &desc, desc_pa, i);
} }
/* Collect all the descriptors */ /* Collect all the descriptors */
do { do {
hwaddr pa = vring_desc_addr(vdev, desc_pa, i); if (desc.flags & VRING_DESC_F_WRITE) {
size_t len = vring_desc_len(vdev, desc_pa, i);
if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE) {
virtqueue_map_desc(&in_num, addr + out_num, iov + out_num, virtqueue_map_desc(&in_num, addr + out_num, iov + out_num,
VIRTQUEUE_MAX_SIZE - out_num, true, pa, len); VIRTQUEUE_MAX_SIZE - out_num, true, desc.addr, desc.len);
} else { } else {
if (in_num) { if (in_num) {
error_report("Incorrect order for descriptors"); error_report("Incorrect order for descriptors");
exit(1); exit(1);
} }
virtqueue_map_desc(&out_num, addr, iov, virtqueue_map_desc(&out_num, addr, iov,
VIRTQUEUE_MAX_SIZE, false, pa, len); VIRTQUEUE_MAX_SIZE, false, desc.addr, desc.len);
} }
/* If we've got too many, that implies a descriptor loop. */ /* If we've got too many, that implies a descriptor loop. */
@ -594,7 +578,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
error_report("Looped descriptor"); error_report("Looped descriptor");
exit(1); exit(1);
} }
} while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max); } while ((i = virtqueue_read_next_desc(vdev, &desc, desc_pa, max)) != max);
/* Now copy what we have collected and mapped */ /* Now copy what we have collected and mapped */
elem = virtqueue_alloc_element(sz, out_num, in_num); elem = virtqueue_alloc_element(sz, out_num, in_num);