Hi Yu, Hengqi, First, thanks Yu for testing and reporting the performance degradation, this is much appreciated!
On 7/4/25 1:29 PM, Jiang, YuX wrote:
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.
The options I see are: 1. Revert the patch for v25.07, fix it and resubmit for v25.11. 2. Fix it on time for v25.07-rc3 3. Keep the patch in v25.07 and try to fix it in v25.11. As I will be OoO starting this evening, I would be in favor of option 1. What do you think? Thanks, Maxime
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
