Linux Virtualization - Jul 2020 - [PATCH V2 4/6] vhost_vdpa: implement IRQ offloading in vhost_vdpa

On 2020/7/16 ??7:23, Zhu Lingshan wrote:
> This patch introduce a set of functions for setup/unsetup
> and update irq offloading respectively by register/unregister
> and re-register the irq_bypass_producer.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu at intel.com>
> Suggested-by: Jason Wang <jasowang at redhat.com>
> ---
>   drivers/vhost/Kconfig |  1 +
>   drivers/vhost/vdpa.c  | 48
++++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 49 insertions(+)
>
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index d3688c6..587fbae 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -65,6 +65,7 @@ config VHOST_VDPA
>   	tristate "Vhost driver for vDPA-based backend"
>   	depends on EVENTFD
>   	select VHOST
> +	select IRQ_BYPASS_MANAGER
>   	depends on VDPA
>   	help
>   	  This kernel module can be loaded in host kernel to accelerate
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 2fcc422..b9078d4 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -115,6 +115,43 @@ static irqreturn_t vhost_vdpa_config_cb(void *private)
>   	return IRQ_HANDLED;
>   }
>   
> +static void vhost_vdpa_setup_vq_irq(struct vdpa_device *dev, int qid, int
irq)
> +{
> +	struct vhost_vdpa *v = vdpa_get_drvdata(dev);
> +	struct vhost_virtqueue *vq = &v->vqs[qid];
> +	int ret;
> +
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	if (!vq->call_ctx.ctx) {
> +		spin_unlock(&vq->call_ctx.ctx_lock);
> +		return;
> +	}

I think we can simply remove this check as what is done in 
vhost_vdpq_update_vq_irq().

> +
> +	vq->call_ctx.producer.token = vq->call_ctx.ctx;
> +	vq->call_ctx.producer.irq = irq;
> +	ret = irq_bypass_register_producer(&vq->call_ctx.producer);
> +	spin_unlock(&vq->call_ctx.ctx_lock);
> +}
> +
> +static void vhost_vdpa_unsetup_vq_irq(struct vdpa_device *dev, int qid)
> +{
> +	struct vhost_vdpa *v = vdpa_get_drvdata(dev);
> +	struct vhost_virtqueue *vq = &v->vqs[qid];
> +
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	irq_bypass_unregister_producer(&vq->call_ctx.producer);
> +	spin_unlock(&vq->call_ctx.ctx_lock);
> +}
> +
> +static void vhost_vdpa_update_vq_irq(struct vhost_virtqueue *vq)
> +{
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	irq_bypass_unregister_producer(&vq->call_ctx.producer);
> +	vq->call_ctx.producer.token = vq->call_ctx.ctx;
> +	irq_bypass_register_producer(&vq->call_ctx.producer);
> +	spin_unlock(&vq->call_ctx.ctx_lock);
> +}
> +
>   static void vhost_vdpa_reset(struct vhost_vdpa *v)
>   {
>   	struct vdpa_device *vdpa = v->vdpa;
> @@ -332,6 +369,7 @@ static long vhost_vdpa_set_config_call(struct
vhost_vdpa *v, u32 __user *argp)
>   
>   	return 0;
>   }
> +

If you really want to fix coding style issue, it's better to have 
another patch.

>   static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int
cmd,
>   				   void __user *argp)
>   {
> @@ -390,6 +428,14 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa
*v, unsigned int cmd,
>   			cb.private = NULL;
>   		}
>   		ops->set_vq_cb(vdpa, idx, &cb);
> +		/*
> +		 * if it has a non-zero irq, means there is a
> +		 * previsouly registered irq_bypass_producer,
> +		 * we should update it when ctx (its token)
> +		 * changes.
> +		 */
> +		if (vq->call_ctx.producer.irq)
> +			vhost_vdpa_update_vq_irq(vq);

Is this safe to check producer.irq outside spinlock?

Thanks

>   		break;
>   
>   	case VHOST_SET_VRING_NUM:
> @@ -951,6 +997,8 @@ static void vhost_vdpa_remove(struct vdpa_device *vdpa)
>   	},
>   	.probe	= vhost_vdpa_probe,
>   	.remove	= vhost_vdpa_remove,
> +	.setup_vq_irq = vhost_vdpa_setup_vq_irq,
> +	.unsetup_vq_irq = vhost_vdpa_unsetup_vq_irq,
>   };
>   
>   static int __init vhost_vdpa_init(void)