[dpdk-dev] mbuf cleanup in i40e/ixgbe
Commit Message
Hello
I'm checking mbuf consumption issues in TX path and it looks like i40e and
ixgbe drivers consume all mbufs in "full featured" path and free them one-by-
one only after TX queue wraps.
Upstream drivers are more conservative with memory consumption and free up to
256 SKBs on every napi_poll invocation. And this makes sense because there is
indeed not too much work for cleanup and freeing as much memory buffers as
possible would lower memory pressure and memory requirements and allow bigger
TX bursts without cleanup procedures and better CPU cache utilization.
Why cannot we bulk free mbuf in i40e_xmit_cleanup ? Why do we need
nb_tx_to_clean calculations? Isn't it always equal to txq->tx_rs_thresh?
Here is a proposed patch for i40e PMD to bulk free unused mbufs:
----------------------------------- CUT --------------------------------------
----------------------------------- CUT --------------------------------------
What do you think about cleaning not just txq->tx_rs_thresh mbufs but as many
as possible?
Regards, Evgeniy Marchenko
DDoS-Guard.net
@@ -883,8 +883,12 @@ i40e_xmit_cleanup(struct i40e_tx_queue *txq)
uint16_t nb_tx_desc = txq->nb_tx_desc;
uint16_t desc_to_clean_to;
uint16_t nb_tx_to_clean;
+ struct i40e_tx_entry *txe;
+ int i;
- desc_to_clean_to = (uint16_t)(last_desc_cleaned + txq->tx_rs_thresh);
+ nb_tx_to_clean = txq->tx_rs_thresh;
+
+ desc_to_clean_to = (uint16_t)(last_desc_cleaned + nb_tx_to_clean);
if (desc_to_clean_to >= nb_tx_desc)
desc_to_clean_to = (uint16_t)(desc_to_clean_to - nb_tx_desc);
@@ -898,12 +902,18 @@ i40e_xmit_cleanup(struct i40e_tx_queue *txq)
return -1;
}
- if (last_desc_cleaned > desc_to_clean_to)
- nb_tx_to_clean = (uint16_t)((nb_tx_desc - last_desc_cleaned) +
- desc_to_clean_to);
- else
- nb_tx_to_clean = (uint16_t)(desc_to_clean_to -
- last_desc_cleaned);
+ i = last_desc_cleaned;
+ while (i++ != desc_to_clean_to) {
+ if (i >= nb_tx_desc)
+ i -= nb_tx_desc;
+
+ txe = &sw_ring[i];
+ RTE_MBUF_PREFETCH_TO_FREE(txe->mbuf);
+ if (txe->mbuf) {
+ rte_pktmbuf_free_seg(txe->mbuf);
+ txe->mbuf = NULL;
+ }
+ }
txd[desc_to_clean_to].cmd_type_offset_bsz = 0;