Messages in this thread Patch in this message | | | Subject | Re: [RFC v3 4/5] virtio_ring: add event idx support in packed ring | From | Jason Wang <> | Date | Wed, 16 May 2018 13:01:04 +0800 |
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On 2018年04月25日 13:15, Tiwei Bie wrote: > This commit introduces the event idx support in packed > ring. This feature is temporarily disabled, because the > implementation in this patch may not work as expected, > and some further discussions on the implementation are > needed, e.g. do we have to check the wrap counter when > checking whether a kick is needed? > > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com> > --- > drivers/virtio/virtio_ring.c | 53 ++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 49 insertions(+), 4 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 0181e93897be..b1039c2985b9 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -986,7 +986,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > - u16 flags; > + u16 new, old, off_wrap, flags; > bool needs_kick; > u32 snapshot; > > @@ -995,7 +995,12 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > * suppressions. */ > virtio_mb(vq->weak_barriers); > > + old = vq->next_avail_idx - vq->num_added; > + new = vq->next_avail_idx; > + vq->num_added = 0; > + > snapshot = *(u32 *)vq->vring_packed.device; > + off_wrap = virtio16_to_cpu(_vq->vdev, snapshot & 0xffff); > flags = cpu_to_virtio16(_vq->vdev, snapshot >> 16) & 0x3; > > #ifdef DEBUG > @@ -1006,7 +1011,10 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > vq->last_add_time_valid = false; > #endif > > - needs_kick = (flags != VRING_EVENT_F_DISABLE); > + if (flags == VRING_EVENT_F_DESC) > + needs_kick = vring_need_event(off_wrap & ~(1<<15), new, old); > + else > + needs_kick = (flags != VRING_EVENT_F_DISABLE); > END_USE(vq); > return needs_kick; > } > @@ -1116,6 +1124,15 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > if (vq->last_used_idx >= vq->vring_packed.num) > vq->last_used_idx -= vq->vring_packed.num; > > + /* If we expect an interrupt for the next entry, tell host > + * by writing event index and flush out the write before > + * the read in the next get_buf call. */ > + if (vq->event_flags_shadow == VRING_EVENT_F_DESC) > + virtio_store_mb(vq->weak_barriers, > + &vq->vring_packed.driver->off_wrap, > + cpu_to_virtio16(_vq->vdev, vq->last_used_idx | > + (vq->wrap_counter << 15))); > + > #ifdef DEBUG > vq->last_add_time_valid = false; > #endif > @@ -1143,10 +1160,17 @@ static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > /* We optimistically turn back on interrupts, then check if there was > * more to do. */ > + /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to > + * either clear the flags bit or point the event index at the next > + * entry. Always update the event index to keep code simple. */ > + > + vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev, > + vq->last_used_idx | (vq->wrap_counter << 15));
Using vq->wrap_counter seems not correct, what we need is the warp counter for the last_used_idx not next_avail_idx.
And I think there's even no need to bother with event idx here, how about just set VRING_EVENT_F_ENABLE?
> > if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > virtio_wmb(vq->weak_barriers); > - vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > + vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC : > + VRING_EVENT_F_ENABLE; > vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > vq->event_flags_shadow); > } > @@ -1172,15 +1196,34 @@ static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned last_used_idx) > static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > + u16 bufs, used_idx, wrap_counter; > > START_USE(vq); > > /* We optimistically turn back on interrupts, then check if there was > * more to do. */ > + /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to > + * either clear the flags bit or point the event index at the next > + * entry. Always update the event index to keep code simple. */ > + > + /* TODO: tune this threshold */ > + bufs = (u16)(vq->next_avail_idx - vq->last_used_idx) * 3 / 4;
bufs could be more than vq->num here, is this intended?
> + > + used_idx = vq->last_used_idx + bufs; > + wrap_counter = vq->wrap_counter; > + > + if (used_idx >= vq->vring_packed.num) { > + used_idx -= vq->vring_packed.num; > + wrap_counter ^= 1;
When used_idx is greater or equal vq->num, there's no need to flip warp_counter bit since it should match next_avail_idx.
And we need also care about the case when next_avail wraps but used_idx not. so we probaly need:
else if (vq->next_avail_idx < used_idx) { wrap_counter ^= 1; }
I think maybe it's time to add some sample codes in the spec to avoid duplicating the efforts(bugs).
Thanks > + } > + > + vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev, > + used_idx | (wrap_counter << 15)); > > if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > virtio_wmb(vq->weak_barriers); > - vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > + vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC : > + VRING_EVENT_F_ENABLE; > vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > vq->event_flags_shadow); > } > @@ -1822,8 +1865,10 @@ void vring_transport_features(struct virtio_device *vdev) > switch (i) { > case VIRTIO_RING_F_INDIRECT_DESC: > break; > +#if 0 > case VIRTIO_RING_F_EVENT_IDX: > break; > +#endif > case VIRTIO_F_VERSION_1: > break; > case VIRTIO_F_IOMMU_PLATFORM:
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