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Message-ID: <20250407041729-mutt-send-email-mst@kernel.org>
Date: Mon, 7 Apr 2025 04:20:37 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/19] virtio_ring: introduce virtqueue ops
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 <jasowang@...hat.com>
> ---
> 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.
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?
> +
> 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
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