Hi Hengqi, Can you help to check the ticket: https://bugs.dpdk.org/show_bug.cgi?id=1747? The perf drop is caused by your patch. Thanks so much.
Best regards, Yu Jiang > -----Original Message----- > From: Hengqi Chen <hengqi.c...@gmail.com> > Sent: Monday, June 9, 2025 3:24 PM > To: dev@dpdk.org > Cc: Hengqi Chen <hengqi.c...@gmail.com>; Baoyuan Li > <updo...@sina.com>; Maxime Coquelin <maxime.coque...@redhat.com>; > Chenbo Xia <chen...@nvidia.com> > Subject: [PATCH] net/virtio: Fix check of threshold for Tx freeing > > Like most dirvers, make the fast path of virtio_xmit_cleanup() behave as > described by the comments of rte_eth_txconf::tx_free_thresh ([0]): > Start freeing Tx buffers if there are > less free descriptors than this value. > > The rationale behind this change is that: > * vq->vq_nentries is set during device probe with the queue size specified > by vhost backend, this value does not reflect the real nb_tx_desc > * the real available tx desc is set to vq->vq_free_cnt via the nb_tx_desc > param of rte_eth_tx_queue_setup() API > * so `nb_used > vq->vq_nentries - vq->vq_free_thresh` could never be true > if say nb_tx_desc=2048, vq->vq_nentries=4096, vq->vq_free_thresh=32, > see bug report 1716 ([1]) for details. > > Bugzilla ID: 1716 > > [0]: https://github.com/DPDK/dpdk/commit/72514b5d5543 > [1]: https://bugs.dpdk.org/show_bug.cgi?id=1716 > > Signed-off-by: Baoyuan Li <updo...@sina.com> > Signed-off-by: Hengqi Chen <hengqi.c...@gmail.com> > --- > drivers/net/virtio/virtio_rxtx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/virtio/virtio_rxtx.c > b/drivers/net/virtio/virtio_rxtx.c > index edecd2011f..ab97f03d7d 100644 > --- a/drivers/net/virtio/virtio_rxtx.c > +++ b/drivers/net/virtio/virtio_rxtx.c > @@ -1873,7 +1873,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf > **tx_pkts, uint16_t nb_pkts) > > nb_used = virtqueue_nused(vq); > > - if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh)) > + if (likely(vq->vq_free_cnt < vq->vq_free_thresh)) > virtio_xmit_cleanup(vq, nb_used); > > for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) { > -- > 2.43.5
