* [dpdk-dev] [PATCH] vhost: read last used index once
@ 2021-04-06 16:17 Balazs Nemeth
0 siblings, 0 replies; only message in thread
From: Balazs Nemeth @ 2021-04-06 16:17 UTC (permalink / raw)
To: bnemeth, dev
Instead of calculating the address of a packed descriptor based on the
vq->desc_packed and vq->last_used_idx every time, store that base
address in desc_base. On arm, this saves 176 bytes in code size of
function in which vhost_flush_enqueue_batch_packed gets inlined.
---
lib/librte_vhost/virtio_net.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 179c57b46..f091384a6 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -217,6 +217,8 @@ vhost_flush_enqueue_batch_packed(struct virtio_net *dev,
{
uint16_t i;
uint16_t flags;
+ uint16_t last_used_idx = vq->last_used_idx;
+ struct vring_packed_desc *desc_base = &vq->desc_packed[last_used_idx];
if (vq->shadow_used_idx) {
do_data_copy_enqueue(dev, vq);
@@ -226,16 +228,17 @@ vhost_flush_enqueue_batch_packed(struct virtio_net *dev,
flags = PACKED_DESC_ENQUEUE_USED_FLAG(vq->used_wrap_counter);
vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
- vq->desc_packed[vq->last_used_idx + i].id = ids[i];
- vq->desc_packed[vq->last_used_idx + i].len = lens[i];
+ desc_base[i].id = ids[i];
+ desc_base[i].len = lens[i];
}
rte_atomic_thread_fence(__ATOMIC_RELEASE);
- vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE)
- vq->desc_packed[vq->last_used_idx + i].flags = flags;
+ vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
+ desc_base[i].flags = flags;
+ }
- vhost_log_cache_used_vring(dev, vq, vq->last_used_idx *
+ vhost_log_cache_used_vring(dev, vq, last_used_idx *
sizeof(struct vring_packed_desc),
sizeof(struct vring_packed_desc) *
PACKED_BATCH_SIZE);
--
2.30.2
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