Re: patch 'net/virtio: fix check of threshold for Tx freeing' has been queued to stable release 22.11.9

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Luca,

This patch introduces a performance regression, could you make sure it
is not applied to the v22.11 LTS ?

Thanks,
Maxime

On 6/30/25 2:25 PM, luca.boccassi@gmail.com wrote:
> Hi,
> 
> FYI, your patch has been queued to stable release 22.11.9
> 
> Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
> It will be pushed if I get no objections before 07/02/25. So please
> shout if anyone has objections.
> 
> Also note that after the patch there's a diff of the upstream commit vs the
> patch applied to the branch. This will indicate if there was any rebasing
> needed to apply to the stable branch. If there were code changes for rebasing
> (ie: not only metadata diffs), please double check that the rebase was
> correctly done.
> 
> Queued patches are on a temporary branch at:
> https://github.com/bluca/dpdk-stable
> 
> This queued commit can be viewed at:
> https://github.com/bluca/dpdk-stable/commit/4863a82ac7db22f67294808bc5077b848e057a40
> 
> Thanks.
> 
> Luca Boccassi
> 
> ---
>  From 4863a82ac7db22f67294808bc5077b848e057a40 Mon Sep 17 00:00:00 2001
> From: Hengqi Chen <hengqi.chen@gmail.com>
> Date: Mon, 9 Jun 2025 07:23:47 +0000
> Subject: [PATCH] net/virtio: fix check of threshold for Tx freeing
> 
> [ upstream commit 3e3c7f3fa5ac3f2748a4463d87e73eb28024b401 ]
> 
> Like most drivers, 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.
> 
> [0]: https://github.com/DPDK/dpdk/commit/72514b5d5543
> [1]: https://bugs.dpdk.org/show_bug.cgi?id=1716
> 
> Bugzilla ID: 1716
> Fixes: 72514b5d5543 ("ethdev: fix check of threshold for Tx freeing")
> 
> Signed-off-by: Baoyuan Li <updoing@sina.com>
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>   .mailmap                         | 3 +++
>   drivers/net/virtio/virtio_rxtx.c | 2 +-
>   2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/.mailmap b/.mailmap
> index f53fdf0d85..bda591c1cf 100644
> --- a/.mailmap
> +++ b/.mailmap
> @@ -150,6 +150,8 @@ Balakrishna Bhamidipati <bbhamidipati@marvell.com>
>   Balasubramanian Manoharan <balasubramanian.manoharan@caviumnetworks.com>
>   Balazs Nemeth <bnemeth@redhat.com> <balazs.nemeth@intel.com>
>   Bao-Long Tran <longtb5@viettel.com.vn>
> +Baoyuan Li <updoing@sina.com>
> +Bar Neuman <bneuman@nvidia.com>
>   Barak Enat <barak@saguna.net>
>   Barry Cao <barry.cao@nxp.com>
>   Bartosz Staszewski <bartoszx.staszewski@intel.com>
> @@ -504,6 +506,7 @@ Hemant Agrawal <hemant.agrawal@nxp.com> <hemant@freescale.com>
>   Heng Ding <hengx.ding@intel.com>
>   Hengjian Zhang <hengjianx.zhang@intel.com>
>   Heng Jiang <jiangheng14@huawei.com>
> +Hengqi Chen <hengqi.chen@gmail.com>
>   Heng Wang <heng.wang@ericsson.com>
>   Henning Schild <henning.schild@siemens.com>
>   Henry Cai <caihe@huawei.com>
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index c3e686cf0c..66aaeb3c65 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -1870,7 +1870,7 @@ 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++) {