Hi Eelco, On 3/27/23 14:51, Eelco Chaudron wrote:
This patch adds an operation callback which gets called every time the library wants to call eventfd_write(). This eventfd_write() call could result in a system call, which could potentially block the PMD thread.The callback function can decide whether it's ok to handle the eventfd_write() now or have the newly introduced function, rte_vhost_notify_guest(), called at a later time. This can be used by 3rd party applications, like OVS, to avoid system calls being called as part of the PMD threads.
That's a good idea, please find some comments inline:
Signed-off-by: Eelco Chaudron <echau...@redhat.com> --- lib/vhost/rte_vhost.h | 10 +++++++++- lib/vhost/vhost.c | 21 +++++++++++++++++++++ lib/vhost/vhost.h | 43 ++++++++++++++++++++++++++++--------------- 3 files changed, 58 insertions(+), 16 deletions(-) diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h index 58a5d4be92..af7a394d0f 100644 --- a/lib/vhost/rte_vhost.h +++ b/lib/vhost/rte_vhost.h @@ -298,7 +298,13 @@ struct rte_vhost_device_ops { */ void (*guest_notified)(int vid);- void *reserved[1]; /**< Reserved for future extension */+ /** + * If this callback is registered, notification to the guest can + * be handled by the front-end calling rte_vhost_notify_guest(). + * If it's not handled, 'false' should be returned. This can be used + * to remove the "slow" eventfd_write() syscall from the datapath. + */ + bool (*guest_notify)(int vid, uint16_t queue_id); };/**@@ -433,6 +439,8 @@ void rte_vhost_log_used_vring(int vid, uint16_t vring_idx,int rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable); +void rte_vhost_notify_guest(int vid, uint16_t queue_id);
The new API needs to be tagged as experimental, and also documented. (I see rte_vhost_enable_guest_notification is not properly documented, so not a good example!)
+ /** * Register vhost driver. path could be different for multiple * instance support. diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c index ef37943817..ee090d78ef 100644 --- a/lib/vhost/vhost.c +++ b/lib/vhost/vhost.c @@ -1467,6 +1467,27 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable) return ret; }+void+rte_vhost_notify_guest(int vid, uint16_t queue_id) +{ + struct virtio_net *dev = get_device(vid); + struct vhost_virtqueue *vq; + + if (!dev || queue_id >= VHOST_MAX_VRING) + return; + + vq = dev->virtqueue[queue_id]; + if (!vq) + return; + + rte_spinlock_lock(&vq->access_lock); + + if (vq->callfd >= 0) + eventfd_write(vq->callfd, (eventfd_t)1);
Maybe we should return an error of callfd is invalid or eventfd_write() failed.
+ + rte_spinlock_unlock(&vq->access_lock); +} + void rte_vhost_log_write(int vid, uint64_t addr, uint64_t len) { diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h index 8fdab13c70..39ad8260a1 100644 --- a/lib/vhost/vhost.h +++ b/lib/vhost/vhost.h @@ -883,6 +883,30 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old) return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old); }+static __rte_always_inline void+vhost_vring_kick_guest(struct virtio_net *dev, struct vhost_virtqueue *vq) +{ + if (dev->notify_ops->guest_notify) { + uint16_t qid; + for (qid = 0; qid < dev->nr_vring; qid++) { + if (dev->virtqueue[qid] == vq) { + if (dev->notify_ops->guest_notify(dev->vid, + qid)) + goto done; + break; + } + }
Since v22.11, you no more need to iterate through the port's virtqueues,
David introduced index field in vhost_virtuqueue in v22.11 (57e414e3ec29
("vhost: keep a reference to virtqueue index")).
+ } + eventfd_write(vq->callfd, (eventfd_t) 1); + +done: + if (dev->flags & VIRTIO_DEV_STATS_ENABLED) + vq->stats.guest_notifications++; + if (dev->notify_ops->guest_notified) + dev->notify_ops->guest_notified(dev->vid); +}
FYI, I have done almost the same refactoring in the VDUSE series I will soon send: https://gitlab.com/mcoquelin/dpdk-next-virtio/-/commit/7089a8a6d1e89b9db90547eb5b4fef886f24fd5b My version also introduces a new counter in case the notification failed. Maybe we could also have a counter in case the notification has been "offloaded" to the application?
+ + static __rte_always_inline void vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq) { @@ -905,21 +929,13 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq) if ((vhost_need_event(vhost_used_event(vq), new, old) && (vq->callfd >= 0)) || unlikely(!signalled_used_valid)) { - eventfd_write(vq->callfd, (eventfd_t) 1); - if (dev->flags & VIRTIO_DEV_STATS_ENABLED) - vq->stats.guest_notifications++; - if (dev->notify_ops->guest_notified) - dev->notify_ops->guest_notified(dev->vid); + vhost_vring_kick_guest(dev, vq); } } else { /* Kick the guest if necessary. */ if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT) && (vq->callfd >= 0)) { - eventfd_write(vq->callfd, (eventfd_t)1); - if (dev->flags & VIRTIO_DEV_STATS_ENABLED) - vq->stats.guest_notifications++; - if (dev->notify_ops->guest_notified) - dev->notify_ops->guest_notified(dev->vid); + vhost_vring_kick_guest(dev, vq); } } } @@ -971,11 +987,8 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq) if (vhost_need_event(off, new, old)) kick = true; kick: - if (kick) { - eventfd_write(vq->callfd, (eventfd_t)1); - if (dev->notify_ops->guest_notified) - dev->notify_ops->guest_notified(dev->vid); - } + if (kick) + vhost_vring_kick_guest(dev, vq); }static __rte_always_inline void
