Re: [dpdk-dev] [PATCH v5 2/2] examples/vhost: use API to check inflight packets

["Ding, Xuan" <xuan.ding@intel.com>]

Hi Kevin,

> -----Original Message-----
> From: Kevin Traynor <ktraynor@redhat.com>
> Sent: Tuesday, September 28, 2021 5:18 PM
> To: Ding, Xuan <xuan.ding@intel.com>; dev@dpdk.org;
> maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: Hu, Jiayu <jiayu.hu@intel.com>; Jiang, Cheng1 <cheng1.jiang@intel.com>;
> Richardson, Bruce <bruce.richardson@intel.com>; Pai G, Sunil
> <sunil.pai.g@intel.com>; Wang, Yinan <yinan.wang@intel.com>; Yang, YvonneX
> <yvonnex.yang@intel.com>
> Subject: Re: [PATCH v5 2/2] examples/vhost: use API to check inflight packets
> 
> On 28/09/2021 07:24, Xuan Ding wrote:
> > In async data path, call rte_vhost_async_get_inflight_thread_unsafe()
> > API to directly return the number of inflight packets instead of
> > maintaining a local variable.
> >
> > Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> > ---
> >   examples/vhost/main.c | 25 +++++++++++--------------
> >   examples/vhost/main.h |  1 -
> >   2 files changed, 11 insertions(+), 15 deletions(-)
> >
> > diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> > index d0bf1f31e3..3faac6d053 100644
> > --- a/examples/vhost/main.c
> > +++ b/examples/vhost/main.c
> > @@ -842,11 +842,8 @@ complete_async_pkts(struct vhost_dev *vdev)
> >
> >   	complete_count = rte_vhost_poll_enqueue_completed(vdev->vid,
> >   					VIRTIO_RXQ, p_cpl, MAX_PKT_BURST);
> > -	if (complete_count) {
> > +	if (complete_count)
> >   		free_pkts(p_cpl, complete_count);
> > -		__atomic_sub_fetch(&vdev->pkts_inflight, complete_count,
> __ATOMIC_SEQ_CST);
> > -	}
> > -
> >   }
> >
> >   static __rte_always_inline void
> > @@ -886,7 +883,6 @@ drain_vhost(struct vhost_dev *vdev)
> >
> >   		complete_async_pkts(vdev);
> >   		ret = rte_vhost_submit_enqueue_burst(vdev->vid, VIRTIO_RXQ,
> m, nr_xmit);
> > -		__atomic_add_fetch(&vdev->pkts_inflight, ret,
> __ATOMIC_SEQ_CST);
> >
> >   		enqueue_fail = nr_xmit - ret;
> >   		if (enqueue_fail)
> > @@ -1212,7 +1208,6 @@ drain_eth_rx(struct vhost_dev *vdev)
> >   		complete_async_pkts(vdev);
> >   		enqueue_count = rte_vhost_submit_enqueue_burst(vdev->vid,
> >   					VIRTIO_RXQ, pkts, rx_count);
> > -		__atomic_add_fetch(&vdev->pkts_inflight, enqueue_count,
> __ATOMIC_SEQ_CST);
> >
> >   		enqueue_fail = rx_count - enqueue_count;
> >   		if (enqueue_fail)
> > @@ -1338,6 +1333,7 @@ destroy_device(int vid)
> >   	struct vhost_dev *vdev = NULL;
> >   	int lcore;
> >   	uint16_t i;
> 
> > +	int pkts_inflight;
> 
> You can move this down to the block it is used in

Thanks for the suggestion.
I consider calling the unsafe API in while (condition), and there is no need to define this variable.

> 
> >
> >   	TAILQ_FOREACH(vdev, &vhost_dev_list, global_vdev_entry) {
> >   		if (vdev->vid == vid)
> > @@ -1384,13 +1380,13 @@ destroy_device(int vid)
> >
> >   	if (async_vhost_driver) {
> >   		uint16_t n_pkt = 0;
> > -		struct rte_mbuf *m_cpl[vdev->pkts_inflight];
> > +		pkts_inflight = rte_vhost_async_get_inflight_thread_unsafe(vid,
> VIRTIO_RXQ);
> > +		struct rte_mbuf *m_cpl[pkts_inflight];
> >
> > -		while (vdev->pkts_inflight) {
> > +		while (pkts_inflight) {
> >   			n_pkt = rte_vhost_clear_queue_thread_unsafe(vid,
> VIRTIO_RXQ,
> > -						m_cpl, vdev->pkts_inflight);
> > +						m_cpl, pkts_inflight);
> >   			free_pkts(m_cpl, n_pkt);
> > -			__atomic_sub_fetch(&vdev->pkts_inflight, n_pkt,
> __ATOMIC_SEQ_CST);
> 
> This is an infinite loop if there are pkts_inflight, need to recheck
> pkts_inflight in the loop.

Thanks for the catch, will call the unsafe API directly in the while (condition).

> 
> >   		}
> >
> >   		rte_vhost_async_channel_unregister(vid, VIRTIO_RXQ);
> > @@ -1486,6 +1482,7 @@ static int
> >   vring_state_changed(int vid, uint16_t queue_id, int enable)
> >   {
> >   	struct vhost_dev *vdev = NULL;
> > +	int pkts_inflight;
> >
> >   	TAILQ_FOREACH(vdev, &vhost_dev_list, global_vdev_entry) {
> >   		if (vdev->vid == vid)
> > @@ -1500,13 +1497,13 @@ vring_state_changed(int vid, uint16_t queue_id,
> int enable)
> >   	if (async_vhost_driver) {
> >   		if (!enable) {
> >   			uint16_t n_pkt = 0;
> > -			struct rte_mbuf *m_cpl[vdev->pkts_inflight];
> > +			pkts_inflight =
> rte_vhost_async_get_inflight_thread_unsafe(vid, queue_id);
> > +			struct rte_mbuf *m_cpl[pkts_inflight];
> >
> > -			while (vdev->pkts_inflight) {
> > +			while (pkts_inflight) {
> >   				n_pkt =
> rte_vhost_clear_queue_thread_unsafe(vid, queue_id,
> > -							m_cpl, vdev-
> >pkts_inflight);
> > +							m_cpl, pkts_inflight);
> >   				free_pkts(m_cpl, n_pkt);
> > -				__atomic_sub_fetch(&vdev->pkts_inflight,
> n_pkt, __ATOMIC_SEQ_CST);
> 
> Same comments as destroy_device

Same as vring_state_changed.

Regards,
Xuan

> 
> >   			}
> >   		}
> >   	}
> > diff --git a/examples/vhost/main.h b/examples/vhost/main.h
> > index e7b1ac60a6..0ccdce4b4a 100644
> > --- a/examples/vhost/main.h
> > +++ b/examples/vhost/main.h
> > @@ -51,7 +51,6 @@ struct vhost_dev {
> >   	uint64_t features;
> >   	size_t hdr_len;
> >   	uint16_t nr_vrings;
> > -	uint16_t pkts_inflight;
> >   	struct rte_vhost_memory *mem;
> >   	struct device_statistics stats;
> >   	TAILQ_ENTRY(vhost_dev) global_vdev_entry;
> >