linux-kernel - Re: [PATCH v3 08/11] vdpa: Add eventfd for the vdpa callback

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Date:   Thu, 16 Mar 2023 17:25:31 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xie Yongji <xieyongji@...edance.com>, mst@...hat.com,
        tglx@...utronix.de, hch@....de
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 08/11] vdpa: Add eventfd for the vdpa callback


在 2023/2/28 17:41, Xie Yongji 写道:
> Add eventfd for the vdpa callback so that user
> can signal it directly instead of running the
> callback. It will be used for vhost-vdpa case.
>
> Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> ---
>   drivers/vhost/vdpa.c         | 2 ++
>   drivers/virtio/virtio_vdpa.c | 1 +
>   include/linux/vdpa.h         | 3 +++
>   3 files changed, 6 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index dc12dbd5b43b..ae89c0ccc2bb 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -599,9 +599,11 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>   		if (vq->call_ctx.ctx) {
>   			cb.callback = vhost_vdpa_virtqueue_cb;
>   			cb.private = vq;
> +			cb.irq_ctx = vq->call_ctx.ctx;
>   		} else {
>   			cb.callback = NULL;
>   			cb.private = NULL;
> +			cb.irq_ctx = NULL;
>   		}
>   		ops->set_vq_cb(vdpa, idx, &cb);
>   		vhost_vdpa_setup_vq_irq(v, idx);
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index 9eee8afabda8..a5cecafbc2d1 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -195,6 +195,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>   	/* Setup virtqueue callback */
>   	cb.callback = callback ? virtio_vdpa_virtqueue_cb : NULL;
>   	cb.private = info;
> +	cb.irq_ctx = NULL;
>   	ops->set_vq_cb(vdpa, index, &cb);
>   	ops->set_vq_num(vdpa, index, virtqueue_get_vring_size(vq));
>   
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index 10bd22387276..94a7ec49583a 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -13,10 +13,13 @@
>    * struct vdpa_calllback - vDPA callback definition.
>    * @callback: interrupt callback function
>    * @private: the data passed to the callback function
> + * @irq_ctx: the eventfd for the callback, user can signal
> + *           it directly instead of running the callback


I'd suggest to do more tweaks to mention:

1) irq_ctx is optional
2) that when the irq_ctx is set, the vDPA driver must guarantee that 
signaling it is functional equivalent to triggering the callback. When 
set, vDPA parent can signal it directly instead of triggering the callback.

>    */
>   struct vdpa_callback {
>   	irqreturn_t (*callback)(void *data);
>   	void *private;
> +	struct eventfd_ctx *irq_ctx;


There's no IRQ concept at the virtual vDPA bus level, so it's probably 
better to rename it as "trigger".

Btw, should we select EVENTFD for vDPA?

Thanks


>   };
>   
>   /**