Hello,
On 5/27/23 09:08, wangzengyuan wrote:
Hi,
I am writing to inquire about the vring cleanup process during
packets transmission.
In the virtio_xmit_pkts function, there is the following code:
nb_used = virtqueue_nused(vq);
if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
virtio_xmit_cleanup(vq, nb_used);
In other words, cleaning is performed when the number of items used in
the vring exceeds (vq->vq_nentries - vq->vq_free_thresh). In the case of
an vring size of 4096, at least (4096-32) items need to be cleaned at
once, which will take a considerable amount of time.
I'm curious why not clean up fewer items each time to avoid taking up
too much CPU time in one transmission. Because during the debugging
process, I found that cleaning up thousands of items at once takes up a
considerable amount of time.
As I am not familiar with this process, I would appreciate it if you
could provide me with some information on what its purpose is.
Both the Tx and Rx queues free threshold are configurable via ethdev
APIs:
int rte_eth_tx_queue_setup(uint16_t port_id, uint16_t tx_queue_id,
uint16_t nb_tx_desc, unsigned int socket_id,
const struct rte_eth_txconf *tx_conf);
int rte_eth_rx_queue_setup(uint16_t port_id, uint16_t rx_queue_id,
uint16_t nb_rx_desc, unsigned int socket_id,
const struct rte_eth_rxconf *rx_conf,
struct rte_mempool *mb_pool);
As you are using large rings, your application may use above APIs to set
more appropriate values.
Regards,
Maxime
Best regards,
Zengyuan Wang
