[dpdk-dev] [PATCH v2] kni: add new mbuf in alloc_q only based on its empty slots

[Gowrishankar <gowrishankar.m@linux.vnet.ibm.com>]

From: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>

In kni_allocate_mbufs(), we attempt to add max_burst (32) count of mbuf
always into alloc_q, which is excessively leading too many rte_pktmbuf_
free() when alloc_q is contending at high packet rate (for eg 10Gig data).
In a situation when alloc_q fifo can only accommodate very few (or zero)
mbuf, create only what needed and add in fifo.

With this patch, we could stop random network stall in KNI at higher packet
rate (eg 1G or 10G data between vEth0 and PMD) sufficiently exhausting
alloc_q on above condition. I tested i40e PMD for this purpose in ppc64le.

Changes:
 v2 - alloc_q free count calculation corrected.
      line wrap fixed for commit message.

Signed-off-by: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>
---
 lib/librte_kni/rte_kni.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/librte_kni/rte_kni.c b/lib/librte_kni/rte_kni.c
index c3f9208..9c5d485 100644
--- a/lib/librte_kni/rte_kni.c
+++ b/lib/librte_kni/rte_kni.c
@@ -624,6 +624,7 @@ struct rte_kni *
 	int i, ret;
 	struct rte_mbuf *pkts[MAX_MBUF_BURST_NUM];
 	void *phys[MAX_MBUF_BURST_NUM];
+	int allocq_free;
 
 	RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, pool) !=
 			 offsetof(struct rte_kni_mbuf, pool));
@@ -646,7 +647,9 @@ struct rte_kni *
 		return;
 	}
 
-	for (i = 0; i < MAX_MBUF_BURST_NUM; i++) {
+	allocq_free = (kni->alloc_q->read - kni->alloc_q->write - 1) \
+			& (MAX_MBUF_BURST_NUM - 1);
+	for (i = 0; i < allocq_free; i++) {
 		pkts[i] = rte_pktmbuf_alloc(kni->pktmbuf_pool);
 		if (unlikely(pkts[i] == NULL)) {
 			/* Out of memory */
-- 
1.9.1