Re: [Qemu-devel] [[RFC v3 08/12] virtio: event suppression support for packed ring

[Wei Xu <wexu@redhat.com>]

On Mon, Oct 15, 2018 at 02:59:48PM +0800, Jason Wang wrote:
> 
> 
> On 2018年10月11日 22:08, wexu@redhat.com wrote:
> >From: Wei Xu <wexu@redhat.com>
> >
> >Signed-off-by: Wei Xu <wexu@redhat.com>
> >---
> >  hw/virtio/virtio.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 123 insertions(+), 3 deletions(-)
> >
> >diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >index d12a7e3..1d25776 100644
> >--- a/hw/virtio/virtio.c
> >+++ b/hw/virtio/virtio.c
> >@@ -241,6 +241,30 @@ static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
> >      virtio_tswap16s(vdev, &desc->next);
> >  }
> >+static void vring_packed_event_read(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, VRingPackedDescEvent *e)
> >+{
> >+    address_space_read_cached(cache, 0, e, sizeof(*e));
> >+    virtio_tswap16s(vdev, &e->off_wrap);
> >+    virtio_tswap16s(vdev, &e->flags);
> >+}
> >+
> >+static void vring_packed_off_wrap_write(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, uint16_t off_wrap)
> >+{
> >+    virtio_tswap16s(vdev, &off_wrap);
> >+    address_space_write_cached(cache, 0, &off_wrap, sizeof(off_wrap));
> >+    address_space_cache_invalidate(cache, 0, sizeof(off_wrap));
> >+}
> >+
> >+static void vring_packed_flags_write(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, uint16_t flags)
> >+{
> >+    virtio_tswap16s(vdev, &flags);
> >+    address_space_write_cached(cache, sizeof(uint16_t), &flags, sizeof(flags));
> >+    address_space_cache_invalidate(cache, sizeof(uint16_t), sizeof(flags));
> >+}
> >+
> >  static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
> >  {
> >      VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
> >@@ -347,7 +371,7 @@ static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
> >      address_space_cache_invalidate(&caches->used, pa, sizeof(val));
> >  }
> >-void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >+static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
> >  {
> >      vq->notification = enable;
> >@@ -370,6 +394,51 @@ void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >      rcu_read_unlock();
> >  }
> >+static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
> >+{
> >+    VRingPackedDescEvent e;
> >+    VRingMemoryRegionCaches *caches;
> >+
> >+    rcu_read_lock();
> >+    caches  = vring_get_region_caches(vq);
> >+    vring_packed_event_read(vq->vdev, &caches->device, &e);
> >+
> >+    if (!enable) {
> >+        e.flags = RING_EVENT_FLAGS_DISABLE;
> >+        goto out;
> >+    }
> >+
> >+    e.flags = RING_EVENT_FLAGS_ENABLE;
> >+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> >+        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
> 
> Btw, why not just use shadow_avail_idx here?

It is nice to do that but an issue here is that it is 'shadow_avail_idx' for
Rx but 'used_idx' for Tx when setting up for a kick, haven't figured out a
clear fix because it helps easier migration part work, any idea?

Wei

> 
> Thanks
> 
> >+
> >+        vring_packed_off_wrap_write(vq->vdev, &caches->device, off_wrap);
> >+        /* Make sure off_wrap is wrote before flags */
> >+        smp_wmb();
> >+
> >+        e.flags = RING_EVENT_FLAGS_DESC;
> >+    }
> >+
> >+out:
> >+    vring_packed_flags_write(vq->vdev, &caches->device, e.flags);
> >+    rcu_read_unlock();
> >+}
> >+
> >+void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >+{
> >+    vq->notification = enable;
> >+
> >+    if (!vq->vring.desc) {
> >+        return;
> >+    }
> >+
> >+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> >+        virtio_queue_set_notification_packed(vq, enable);
> >+    } else {
> >+        virtio_queue_set_notification_split(vq, enable);
> >+    }
> >+}
> >+
> >  int virtio_queue_ready(VirtQueue *vq)
> >  {
> >      return vq->vring.avail != 0;
> >@@ -2103,8 +2172,7 @@ static void virtio_set_isr(VirtIODevice *vdev, int value)
> >      }
> >  }
> >-/* Called within rcu_read_lock().  */
> >-static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >  {
> >      uint16_t old, new;
> >      bool v;
> >@@ -2127,6 +2195,58 @@ static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >      return !v || vring_need_event(vring_get_used_event(vq), new, old);
> >  }
> >+static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap,
> >+                                    uint16_t new, uint16_t old)
> >+{
> >+    bool wrap = vq->event_wrap_counter;
> >+    int off = off_wrap & ~(1 << 15);
> >+
> >+    if (new < old) {
> >+        new += vq->vring.num;
> >+        wrap ^= 1;
> >+    }
> >+
> >+    if (wrap != off_wrap >> 15) {
> >+        off += vq->vring.num;
> >+    }
> >+
> >+    return vring_need_event(off, new, old);
> >+}
> >+
> >+static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+{
> >+    VRingPackedDescEvent e;
> >+    uint16_t old, new;
> >+    bool v;
> >+    VRingMemoryRegionCaches *caches;
> >+
> >+    caches  = vring_get_region_caches(vq);
> >+    vring_packed_event_read(vdev, &caches->driver, &e);
> >+
> >+    old = vq->signalled_used;
> >+    new = vq->signalled_used = vq->used_idx;
> >+    v = vq->signalled_used_valid;
> >+    vq->signalled_used_valid = true;
> >+
> >+    if (e.flags == RING_EVENT_FLAGS_DISABLE) {
> >+        return false;
> >+    } else if (e.flags == RING_EVENT_FLAGS_ENABLE) {
> >+        return true;
> >+    }
> >+
> >+    return !v || vring_packed_need_event(vq, e.off_wrap, new, old);
> >+}
> >+
> >+/* Called within rcu_read_lock().  */
> >+static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+{
> >+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >+        return virtio_packed_should_notify(vdev, vq);
> >+    } else {
> >+        return virtio_split_should_notify(vdev, vq);
> >+    }
> >+}
> >+
> >  void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
> >  {
> >      bool should_notify;
>