Xuan Zhuo
2022-Jul-28 08:09 UTC
[PATCH v13 16/42] virtio_ring: split: introduce virtqueue_resize_split()
On Thu, 28 Jul 2022 15:42:50 +0800, Jason Wang <jasowang at redhat.com> wrote:> On Thu, Jul 28, 2022 at 3:24 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote: > > > > On Thu, 28 Jul 2022 10:38:51 +0800, Jason Wang <jasowang at redhat.com> wrote: > > > On Wed, Jul 27, 2022 at 3:44 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote: > > > > > > > > On Wed, 27 Jul 2022 11:12:19 +0800, Jason Wang <jasowang at redhat.com> wrote: > > > > > > > > > > ? 2022/7/26 15:21, Xuan Zhuo ??: > > > > > > virtio ring split supports resize. > > > > > > > > > > > > Only after the new vring is successfully allocated based on the new num, > > > > > > we will release the old vring. In any case, an error is returned, > > > > > > indicating that the vring still points to the old vring. > > > > > > > > > > > > In the case of an error, re-initialize(virtqueue_reinit_split()) the > > > > > > virtqueue to ensure that the vring can be used. > > > > > > > > > > > > Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com> > > > > > > Acked-by: Jason Wang <jasowang at redhat.com> > > > > > > --- > > > > > > drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++++++++++ > > > > > > 1 file changed, 34 insertions(+) > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > > > index b6fda91c8059..58355e1ac7d7 100644 > > > > > > --- a/drivers/virtio/virtio_ring.c > > > > > > +++ b/drivers/virtio/virtio_ring.c > > > > > > @@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index, > > > > > > void (*callback)(struct virtqueue *), > > > > > > const char *name); > > > > > > static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num); > > > > > > +static void vring_free(struct virtqueue *_vq); > > > > > > > > > > > > /* > > > > > > * Helpers. > > > > > > @@ -1117,6 +1118,39 @@ static struct virtqueue *vring_create_virtqueue_split( > > > > > > return vq; > > > > > > } > > > > > > > > > > > > +static int virtqueue_resize_split(struct virtqueue *_vq, u32 num) > > > > > > +{ > > > > > > + struct vring_virtqueue_split vring_split = {}; > > > > > > + struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + struct virtio_device *vdev = _vq->vdev; > > > > > > + int err; > > > > > > + > > > > > > + err = vring_alloc_queue_split(&vring_split, vdev, num, > > > > > > + vq->split.vring_align, > > > > > > + vq->split.may_reduce_num); > > > > > > + if (err) > > > > > > + goto err; > > > > > > > > > > > > > > > I think we don't need to do anything here? > > > > > > > > Am I missing something? > > > > > > I meant it looks to me most of the virtqueue_reinit() is unnecessary. > > > We probably only need to reinit avail/used idx there. > > > > > > In this function, we can indeed remove some code. > > > > > static void virtqueue_reinit_split(struct vring_virtqueue *vq) > > > { > > > int size, i; > > > > > > memset(vq->split.vring.desc, 0, vq->split.queue_size_in_bytes); > > > > > > size = sizeof(struct vring_desc_state_split) * vq->split.vring.num; > > > memset(vq->split.desc_state, 0, size); > > > > > > size = sizeof(struct vring_desc_extra) * vq->split.vring.num; > > > memset(vq->split.desc_extra, 0, size); > > > > These memsets can be removed, and theoretically it will not cause any > > exceptions. > > Yes, otherwise we have bugs in detach_buf(). > > > > > > > > > > > > > > > for (i = 0; i < vq->split.vring.num - 1; i++) > > > vq->split.desc_extra[i].next = i + 1; > > > > This can also be removed, but we need to record free_head that will been update > > inside virtqueue_init(). > > We can simply keep free_head unchanged? Otherwise it's a bug somewhere I guess. > > > > > > > > > > virtqueue_init(vq, vq->split.vring.num); > > > > There are some operations in this, which can also be skipped, such as setting > > use_dma_api. But I think calling this function directly will be more convenient > > for maintenance. > > I don't see anything that is necessary here.These three are currently inside virtqueue_init() vq->last_used_idx = 0; vq->event_triggered = false; vq->num_added = 0; Thanks.> > > > > > > > virtqueue_vring_init_split(&vq->split, vq); > > > > virtqueue_vring_init_split() is necessary. > > Right. > > > > > > } > > > > Another method, we can take out all the variables to be reinitialized > > separately, and repackage them into a new function. I don?t think it?s worth > > it, because this path will only be reached if the memory allocation fails, which > > is a rare occurrence. In this case, doing so will increase the cost of > > maintenance. If you think so also, I will remove the above memset in the next > > version. > > I agree. > > Thanks > > > > > Thanks. > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > + > > > > > > + err = vring_alloc_state_extra_split(&vring_split); > > > > > > + if (err) { > > > > > > + vring_free_split(&vring_split, vdev); > > > > > > + goto err; > > > > > > > > > > > > > > > I suggest to move vring_free_split() into a dedicated error label. > > > > > > > > Will change. > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > + } > > > > > > + > > > > > > + vring_free(&vq->vq); > > > > > > + > > > > > > + virtqueue_vring_init_split(&vring_split, vq); > > > > > > + > > > > > > + virtqueue_init(vq, vring_split.vring.num); > > > > > > + virtqueue_vring_attach_split(vq, &vring_split); > > > > > > + > > > > > > + return 0; > > > > > > + > > > > > > +err: > > > > > > + virtqueue_reinit_split(vq); > > > > > > + return -ENOMEM; > > > > > > +} > > > > > > + > > > > > > > > > > > > /* > > > > > > * Packed ring specific functions - *_packed(). > > > > > > > > > > > > > > >
Jason Wang
2022-Jul-28 09:04 UTC
[PATCH v13 16/42] virtio_ring: split: introduce virtqueue_resize_split()
On Thu, Jul 28, 2022 at 4:18 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote:> > On Thu, 28 Jul 2022 15:42:50 +0800, Jason Wang <jasowang at redhat.com> wrote: > > On Thu, Jul 28, 2022 at 3:24 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote: > > > > > > On Thu, 28 Jul 2022 10:38:51 +0800, Jason Wang <jasowang at redhat.com> wrote: > > > > On Wed, Jul 27, 2022 at 3:44 PM Xuan Zhuo <xuanzhuo at linux.alibaba.com> wrote: > > > > > > > > > > On Wed, 27 Jul 2022 11:12:19 +0800, Jason Wang <jasowang at redhat.com> wrote: > > > > > > > > > > > > ? 2022/7/26 15:21, Xuan Zhuo ??: > > > > > > > virtio ring split supports resize. > > > > > > > > > > > > > > Only after the new vring is successfully allocated based on the new num, > > > > > > > we will release the old vring. In any case, an error is returned, > > > > > > > indicating that the vring still points to the old vring. > > > > > > > > > > > > > > In the case of an error, re-initialize(virtqueue_reinit_split()) the > > > > > > > virtqueue to ensure that the vring can be used. > > > > > > > > > > > > > > Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com> > > > > > > > Acked-by: Jason Wang <jasowang at redhat.com> > > > > > > > --- > > > > > > > drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++++++++++ > > > > > > > 1 file changed, 34 insertions(+) > > > > > > > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > > > > index b6fda91c8059..58355e1ac7d7 100644 > > > > > > > --- a/drivers/virtio/virtio_ring.c > > > > > > > +++ b/drivers/virtio/virtio_ring.c > > > > > > > @@ -220,6 +220,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index, > > > > > > > void (*callback)(struct virtqueue *), > > > > > > > const char *name); > > > > > > > static struct vring_desc_extra *vring_alloc_desc_extra(unsigned int num); > > > > > > > +static void vring_free(struct virtqueue *_vq); > > > > > > > > > > > > > > /* > > > > > > > * Helpers. > > > > > > > @@ -1117,6 +1118,39 @@ static struct virtqueue *vring_create_virtqueue_split( > > > > > > > return vq; > > > > > > > } > > > > > > > > > > > > > > +static int virtqueue_resize_split(struct virtqueue *_vq, u32 num) > > > > > > > +{ > > > > > > > + struct vring_virtqueue_split vring_split = {}; > > > > > > > + struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > > + struct virtio_device *vdev = _vq->vdev; > > > > > > > + int err; > > > > > > > + > > > > > > > + err = vring_alloc_queue_split(&vring_split, vdev, num, > > > > > > > + vq->split.vring_align, > > > > > > > + vq->split.may_reduce_num); > > > > > > > + if (err) > > > > > > > + goto err; > > > > > > > > > > > > > > > > > > I think we don't need to do anything here? > > > > > > > > > > Am I missing something? > > > > > > > > I meant it looks to me most of the virtqueue_reinit() is unnecessary. > > > > We probably only need to reinit avail/used idx there. > > > > > > > > > In this function, we can indeed remove some code. > > > > > > > static void virtqueue_reinit_split(struct vring_virtqueue *vq) > > > > { > > > > int size, i; > > > > > > > > memset(vq->split.vring.desc, 0, vq->split.queue_size_in_bytes); > > > > > > > > size = sizeof(struct vring_desc_state_split) * vq->split.vring.num; > > > > memset(vq->split.desc_state, 0, size); > > > > > > > > size = sizeof(struct vring_desc_extra) * vq->split.vring.num; > > > > memset(vq->split.desc_extra, 0, size); > > > > > > These memsets can be removed, and theoretically it will not cause any > > > exceptions. > > > > Yes, otherwise we have bugs in detach_buf(). > > > > > > > > > > > > > > > > > > > > > for (i = 0; i < vq->split.vring.num - 1; i++) > > > > vq->split.desc_extra[i].next = i + 1; > > > > > > This can also be removed, but we need to record free_head that will been update > > > inside virtqueue_init(). > > > > We can simply keep free_head unchanged? Otherwise it's a bug somewhere I guess. > > > > > > > > > > > > > > > virtqueue_init(vq, vq->split.vring.num); > > > > > > There are some operations in this, which can also be skipped, such as setting > > > use_dma_api. But I think calling this function directly will be more convenient > > > for maintenance. > > > > I don't see anything that is necessary here. > > These three are currently inside virtqueue_init() > > vq->last_used_idx = 0; > vq->event_triggered = false; > vq->num_added = 0;Right. Let's keep it there. (Though it's kind of strange that the last_used_idx is not initialized at the same place with avail_idx/flags_shadow, we can optimize it on top). Thanks> > Thanks. > > > > > > > > > > > > > > virtqueue_vring_init_split(&vq->split, vq); > > > > > > virtqueue_vring_init_split() is necessary. > > > > Right. > > > > > > > > > } > > > > > > Another method, we can take out all the variables to be reinitialized > > > separately, and repackage them into a new function. I don?t think it?s worth > > > it, because this path will only be reached if the memory allocation fails, which > > > is a rare occurrence. In this case, doing so will increase the cost of > > > maintenance. If you think so also, I will remove the above memset in the next > > > version. > > > > I agree. > > > > Thanks > > > > > > > > Thanks. > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > + > > > > > > > + err = vring_alloc_state_extra_split(&vring_split); > > > > > > > + if (err) { > > > > > > > + vring_free_split(&vring_split, vdev); > > > > > > > + goto err; > > > > > > > > > > > > > > > > > > I suggest to move vring_free_split() into a dedicated error label. > > > > > > > > > > Will change. > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > + } > > > > > > > + > > > > > > > + vring_free(&vq->vq); > > > > > > > + > > > > > > > + virtqueue_vring_init_split(&vring_split, vq); > > > > > > > + > > > > > > > + virtqueue_init(vq, vring_split.vring.num); > > > > > > > + virtqueue_vring_attach_split(vq, &vring_split); > > > > > > > + > > > > > > > + return 0; > > > > > > > + > > > > > > > +err: > > > > > > > + virtqueue_reinit_split(vq); > > > > > > > + return -ENOMEM; > > > > > > > +} > > > > > > > + > > > > > > > > > > > > > > /* > > > > > > > * Packed ring specific functions - *_packed(). > > > > > > > > > > > > > > > > > > > > >