From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [RFC v4 4/5] virtio_ring: add event idx support in packed ring Date: Wed, 16 May 2018 20:17:21 +0800 Message-ID: <64f5085b-4b62-d545-36e0-0951c11b29a8@redhat.com> References: <20180516083737.26504-1-tiwei.bie@intel.com> <20180516083737.26504-5-tiwei.bie@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: wexu@redhat.com, jfreimann@redhat.com To: Tiwei Bie , mst@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Return-path: In-Reply-To: <20180516083737.26504-5-tiwei.bie@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2018年05月16日 16:37, Tiwei Bie wrote: > This commit introduces the event idx support in > packed ring. > > Signed-off-by: Tiwei Bie > --- > drivers/virtio/virtio_ring.c | 75 +++++++++++++++++++++++++++++++++--- > 1 file changed, 70 insertions(+), 5 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index c6c5deb0e3ae..de3839f3621a 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -1006,7 +1006,7 @@ 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, wrap_counter, event_idx; > bool needs_kick; > u32 snapshot; > > @@ -1015,9 +1015,19 @@ 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, (__virtio16)(snapshot & 0xffff)); > flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; > > + wrap_counter = off_wrap >> 15; > + event_idx = off_wrap & ~(1<<15); > + if (wrap_counter != vq->wrap_counter) > + event_idx -= vq->vring_packed.num; > + > #ifdef DEBUG > if (vq->last_add_time_valid) { > WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), > @@ -1026,7 +1036,10 @@ 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(event_idx, new, old); > + else > + needs_kick = (flags != VRING_EVENT_F_DISABLE); > END_USE(vq); > return needs_kick; > } > @@ -1098,7 +1111,7 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > void **ctx) > { > struct vring_virtqueue *vq = to_vvq(_vq); > - u16 last_used, id; > + u16 wrap_counter, last_used, id; > void *ret; > > START_USE(vq); > @@ -1138,6 +1151,19 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > ret = vq->desc_state[id].data; > detach_buf_packed(vq, last_used, id, ctx); > > + wrap_counter = vq->wrap_counter; > + if (vq->last_used_idx > vq->next_avail_idx) > + wrap_counter ^= 1; > + > + /* 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 | > + (wrap_counter << 15))); > + > #ifdef DEBUG > vq->last_add_time_valid = false; > #endif > @@ -1160,15 +1186,27 @@ static void virtqueue_disable_cb_packed(struct virtqueue *_vq) > static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > + u16 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. */ > + > + wrap_counter = vq->wrap_counter; > + if (vq->last_used_idx > vq->next_avail_idx) Should this be ">=" consider rx refill may try to completely fill the ring? > + wrap_counter ^= 1; > + > + vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev, > + vq->last_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); > } > @@ -1194,15 +1232,40 @@ 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 */ > + if (vq->next_avail_idx < vq->last_used_idx) > + bufs = (vq->vring_packed.num + vq->next_avail_idx - > + vq->last_used_idx) * 3 / 4; > + else > + bufs = (vq->next_avail_idx - vq->last_used_idx) * 3 / 4; > + > + wrap_counter = vq->wrap_counter; > + if (vq->last_used_idx > vq->next_avail_idx) > + wrap_counter ^= 1; > + > + used_idx = vq->last_used_idx + bufs; > + if (used_idx >= vq->vring_packed.num) { > + used_idx -= vq->vring_packed.num; > + wrap_counter ^= 1; > + } Looks correct but maybe it's better to add some comments for such logic. > + > + 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); > } > @@ -1869,8 +1932,10 @@ 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 Maybe it's time to remove this #if 0. Thanks > case VIRTIO_F_VERSION_1: > break; > case VIRTIO_F_IOMMU_PLATFORM: