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Tsirkin" To: Jason Wang Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 13/19] virtio_ring: introduce virtqueue ops Message-ID: <20250408073317-mutt-send-email-mst@kernel.org> References: <20250324054333.1954-1-jasowang@redhat.com> <20250324060127.2358-1-jasowang@redhat.com> <20250407041729-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CAHUJCEm8TdZU-WA8IgJJb3BmPKGfPkvKNUKNxf7iPQ_1744112219 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Tue, Apr 08, 2025 at 03:02:35PM +0800, Jason Wang wrote: > On Mon, Apr 7, 2025 at 4:20 PM Michael S. Tsirkin wrote: > > > > On Mon, Mar 24, 2025 at 02:01:21PM +0800, Jason Wang wrote: > > > This patch introduces virtqueue ops which is a set of the callbacks > > > that will be called for different queue layout or features. This would > > > help to avoid branches for split/packed and will ease the future > > > implementation like in order. > > > > > > Signed-off-by: Jason Wang > > > > > > > > > > > --- > > > drivers/virtio/virtio_ring.c | 96 +++++++++++++++++++++++++----------- > > > 1 file changed, 67 insertions(+), 29 deletions(-) > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > index a2884eae14d9..ce1dc90ee89d 100644 > > > --- a/drivers/virtio/virtio_ring.c > > > +++ b/drivers/virtio/virtio_ring.c > > > @@ -159,9 +159,30 @@ struct vring_virtqueue_packed { > > > size_t event_size_in_bytes; > > > }; > > > > > > +struct vring_virtqueue; > > > + > > > +struct virtqueue_ops { > > > + int (*add)(struct vring_virtqueue *_vq, struct scatterlist *sgs[], > > > + unsigned int total_sg, unsigned int out_sgs, > > > + unsigned int in_sgs, void *data, > > > + void *ctx, bool premapped, gfp_t gfp); > > > + void *(*get)(struct vring_virtqueue *vq, unsigned int *len, void **ctx); > > > + bool (*kick_prepare)(struct vring_virtqueue *vq); > > > + void (*disable_cb)(struct vring_virtqueue *vq); > > > + bool (*enable_cb_delayed)(struct vring_virtqueue *vq); > > > + unsigned int (*enable_cb_prepare)(struct vring_virtqueue *vq); > > > + bool (*poll)(const struct vring_virtqueue *vq, u16 last_used_idx); > > > + void *(*detach_unused_buf)(struct vring_virtqueue *vq); > > > + bool (*more_used)(const struct vring_virtqueue *vq); > > > + int (*resize)(struct vring_virtqueue *vq, u32 num); > > > + void (*reset)(struct vring_virtqueue *vq); > > > +}; > > > > I like it that it's organized but > > I worry about the overhead of indirect calls here. > > We can switch to use INDIRECT_CALL_X() here If you think it's cleaner.. but INDIRECT_CALL is all chained while a switch can do a binary search. > (but I'm not sure we > should worry about it too much as ndo_ops or qdiscs doesn't use that). And that's why we ended up with xdp, no? the stack's too heavy ... > > How about a switch statement instead? > > > > struct vring_virtqueue { > > enum vring_virtqueue_ops ops; > > > > } > > > > > > @@ -2248,10 +2303,8 @@ static inline int virtqueue_add(struct virtqueue *_vq, > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > switch (vq->ops) { > > VQ_PACKED: > > VQ_SPLIT: > > VQ_IN_ORDER: > > } > > > > > > } > > > > > > What do you think? > > Actually, the matrix will be 2*2: > > PACKED, SPLIT, PACKED_IN_ORDER, SPLIT_IN_ORDER Confused. Same amount of enums as ops structures in your approach, no? > And will be doubled if a new layout is implemented. > > If we open them such a switch will spread in a lot of places in the code. > > Thanks > > > > > > > > > > + > > > struct vring_virtqueue { > > > struct virtqueue vq; > > > > > > + struct virtqueue_ops *ops; > > > + > > > /* Is this a packed ring? */ > > > bool packed_ring; > > > > > > @@ -1116,6 +1137,8 @@ static int vring_alloc_queue_split(struct vring_virtqueue_split *vring_split, > > > return 0; > > > } > > > > > > +struct virtqueue_ops split_ops; > > > + > > > static struct virtqueue *__vring_new_virtqueue_split(unsigned int index, > > > struct vring_virtqueue_split *vring_split, > > > struct virtio_device *vdev, > > > @@ -1134,6 +1157,7 @@ static struct virtqueue *__vring_new_virtqueue_split(unsigned int index, > > > return NULL; > > > > > > vq->packed_ring = false; > > > + vq->ops = &split_ops; > > > vq->vq.callback = callback; > > > vq->vq.vdev = vdev; > > > vq->vq.name = name; > > > @@ -2076,6 +2100,8 @@ static void virtqueue_reset_packed(struct vring_virtqueue *vq) > > > virtqueue_vring_init_packed(&vq->packed, !!vq->vq.callback); > > > } > > > > > > +struct virtqueue_ops packed_ops; > > > + > > > static struct virtqueue *__vring_new_virtqueue_packed(unsigned int index, > > > struct vring_virtqueue_packed *vring_packed, > > > struct virtio_device *vdev, > > > @@ -2107,6 +2133,7 @@ static struct virtqueue *__vring_new_virtqueue_packed(unsigned int index, > > > vq->broken = false; > > > #endif > > > vq->packed_ring = true; > > > + vq->ops = &packed_ops; > > > vq->dma_dev = dma_dev; > > > vq->use_dma_api = vring_use_dma_api(vdev); > > > > > > @@ -2194,6 +2221,34 @@ static int virtqueue_resize_packed(struct vring_virtqueue *vq, u32 num) > > > return -ENOMEM; > > > } > > > > > > +struct virtqueue_ops split_ops = { > > > + .add = virtqueue_add_split, > > > + .get = virtqueue_get_buf_ctx_split, > > > + .kick_prepare = virtqueue_kick_prepare_split, > > > + .disable_cb = virtqueue_disable_cb_split, > > > + .enable_cb_delayed = virtqueue_enable_cb_delayed_split, > > > + .enable_cb_prepare = virtqueue_enable_cb_prepare_split, > > > + .poll = virtqueue_poll_split, > > > + .detach_unused_buf = virtqueue_detach_unused_buf_split, > > > + .more_used = more_used_split, > > > + .resize = virtqueue_resize_split, > > > + .reset = virtqueue_reset_split, > > > +}; > > > + > > > +struct virtqueue_ops packed_ops = { > > > + .add = virtqueue_add_packed, > > > + .get = virtqueue_get_buf_ctx_packed, > > > + .kick_prepare = virtqueue_kick_prepare_packed, > > > + .disable_cb = virtqueue_disable_cb_packed, > > > + .enable_cb_delayed = virtqueue_enable_cb_delayed_packed, > > > + .enable_cb_prepare = virtqueue_enable_cb_prepare_packed, > > > + .poll = virtqueue_poll_packed, > > > + .detach_unused_buf = virtqueue_detach_unused_buf_packed, > > > + .more_used = more_used_packed, > > > + .resize = virtqueue_resize_packed, > > > + .reset = virtqueue_reset_packed, > > > +}; > > > + > > > static int virtqueue_disable_and_recycle(struct virtqueue *_vq, > > > void (*recycle)(struct virtqueue *vq, void *buf)) > > > { > > > @@ -2248,10 +2303,8 @@ static inline int virtqueue_add(struct virtqueue *_vq, > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > - return vq->packed_ring ? virtqueue_add_packed(vq, sgs, total_sg, > > > - out_sgs, in_sgs, data, ctx, premapped, gfp) : > > > - virtqueue_add_split(vq, sgs, total_sg, > > > - out_sgs, in_sgs, data, ctx, premapped, gfp); > > > + return vq->ops->add(vq, sgs, total_sg, > > > + out_sgs, in_sgs, data, ctx, premapped, gfp); > > > } > > > > > > /** > > > @@ -2437,8 +2490,7 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > - return vq->packed_ring ? virtqueue_kick_prepare_packed(vq) : > > > - virtqueue_kick_prepare_split(vq); > > > + return vq->ops->kick_prepare(vq); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_kick_prepare); > > > > > > @@ -2508,8 +2560,7 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len, > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > - return vq->packed_ring ? virtqueue_get_buf_ctx_packed(vq, len, ctx) : > > > - virtqueue_get_buf_ctx_split(vq, len, ctx); > > > + return vq->ops->get(vq, len, ctx); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx); > > > > > > @@ -2531,10 +2582,7 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > - if (vq->packed_ring) > > > - virtqueue_disable_cb_packed(vq); > > > - else > > > - virtqueue_disable_cb_split(vq); > > > + return vq->ops->disable_cb(vq); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_disable_cb); > > > > > > @@ -2557,8 +2605,7 @@ unsigned int virtqueue_enable_cb_prepare(struct virtqueue *_vq) > > > if (vq->event_triggered) > > > vq->event_triggered = false; > > > > > > - return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(vq) : > > > - virtqueue_enable_cb_prepare_split(vq); > > > + return vq->ops->enable_cb_prepare(vq); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare); > > > > > > @@ -2579,8 +2626,7 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned int last_used_idx) > > > return false; > > > > > > virtio_mb(vq->weak_barriers); > > > - return vq->packed_ring ? virtqueue_poll_packed(vq, last_used_idx) : > > > - virtqueue_poll_split(vq, last_used_idx); > > > + return vq->ops->poll(vq, last_used_idx); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_poll); > > > > > > @@ -2623,8 +2669,7 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) > > > if (vq->event_triggered) > > > vq->event_triggered = false; > > > > > > - return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(vq) : > > > - virtqueue_enable_cb_delayed_split(vq); > > > + return vq->ops->enable_cb_delayed(vq); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed); > > > > > > @@ -2640,14 +2685,13 @@ void *virtqueue_detach_unused_buf(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > - return vq->packed_ring ? virtqueue_detach_unused_buf_packed(vq) : > > > - virtqueue_detach_unused_buf_split(vq); > > > + return vq->ops->detach_unused_buf(vq); > > > } > > > EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf); > > > > > > static inline bool more_used(const struct vring_virtqueue *vq) > > > { > > > - return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq); > > > + return vq->ops->more_used(vq); > > > } > > > > > > /** > > > @@ -2785,10 +2829,7 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num, > > > if (recycle_done) > > > recycle_done(_vq); > > > > > > - if (vq->packed_ring) > > > - err = virtqueue_resize_packed(vq, num); > > > - else > > > - err = virtqueue_resize_split(vq, num); > > > + err = vq->ops->resize(vq, num); > > > > > > return virtqueue_enable_after_reset(_vq); > > > } > > > @@ -2822,10 +2863,7 @@ int virtqueue_reset(struct virtqueue *_vq, > > > if (recycle_done) > > > recycle_done(_vq); > > > > > > - if (vq->packed_ring) > > > - virtqueue_reset_packed(vq); > > > - else > > > - virtqueue_reset_split(vq); > > > + vq->ops->reset(vq); > > > > > > return virtqueue_enable_after_reset(_vq); > > > } > > > -- > > > 2.42.0 > >