Friendly reminder:
Could somebody please have a look at this patch now that the DPDK
summit is over?
Thanks, Jan
> -----Original Message-----
> From: Jan Scheurich
> Sent: Saturday, 23 September, 2017 22:32
> To: 'dev@dpdk.org' <dev@dpdk.org>
> Subject: [PATCH v3] vhost: Expose virtio interrupt need on rte_vhost API
>
> Performance tests with the OVS DPDK datapath have shown
> that the tx throughput over a vhostuser port into a VM with
> an interrupt-based virtio driver is limited by the overhead
> incurred by virtio interrupts. The OVS PMD spends up to 30%
> of its cycles in system calls kicking the eventfd. Also the core
> running the vCPU is heavily loaded with generating the virtio
> interrupts in KVM on the host and handling these interrupts
> in the virtio-net driver in the guest. This limits the throughput
> to about 500-700 Kpps with a single vCPU.
>
> OVS is trying to address this issue by batching packets to a
> vhostuser port for some time to limit the virtio interrupt
> frequency. With a 50 us batching period we have measured an
> iperf3 throughput increase by 15% and a PMD utilization
> decrease from 45% to 30%.
>
> On the other hand, guests using virtio PMDs do not profit from
> time-based tx batching. Instead they experience a 2-3%
> performance penalty and an average latency increase of
> 30-40 us. OVS therefore intends to apply time-based tx
> batching only for vhostuser tx queues that need to trigger
> virtio interrupts.
>
> Today this information is hidden inside the rte_vhost library
> and not accessible to users of the API. This patch adds a
> function to the API to query it.
>
> Signed-off-by: Jan Scheurich <jan.scheur...@ericsson.com>
>
> ---
>
> v2 -> v3:
> Fixed even more white-space errors and warnings
> v1 -> v2:
> Fixed too long commit lines
> Fixed white-space errors and warnings
>
> lib/librte_vhost/rte_vhost.h | 12 ++++++++++++
> lib/librte_vhost/vhost.c | 19 +++++++++++++++++++
> 2 files changed, 31 insertions(+)
>
> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
> index 8c974eb..d62338b 100644
> --- a/lib/librte_vhost/rte_vhost.h
> +++ b/lib/librte_vhost/rte_vhost.h
> @@ -444,6 +444,18 @@ int rte_vhost_get_vhost_vring(int vid, uint16_t
> vring_idx,
> */
> uint32_t rte_vhost_rx_queue_count(int vid, uint16_t qid);
>
> +/**
> + * Does the virtio driver request interrupts for a vhost tx queue?
> + *
> + * @param vid
> + * vhost device ID
> + * @param qid
> + * virtio queue index in mq case
> + * @return
> + * 1 if true, 0 if false
> + */
> +int rte_vhost_tx_interrupt_requested(int vid, uint16_t qid);
> +
> #ifdef __cplusplus
> }
> #endif
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 0b6aa1c..c6e636e 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -503,3 +503,22 @@ struct virtio_net *
>
> return *((volatile uint16_t *)&vq->avail->idx) - vq->last_avail_idx;
> }
> +
> +int rte_vhost_tx_interrupt_requested(int vid, uint16_t qid)
> +{
> + struct virtio_net *dev;
> + struct vhost_virtqueue *vq;
> +
> + dev = get_device(vid);
> + if (dev == NULL)
> + return 0;
> +
> + vq = dev->virtqueue[qid];
> + if (vq == NULL)
> + return 0;
> +
> + if (unlikely(vq->enabled == 0 || vq->avail == NULL))
> + return 0;
> +
> + return !(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
> +}
