netdev - Re: [PATCH 3/7] vhost_vdpa: implement IRQ offloading functions in vhost

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Date:   Mon, 13 Jul 2020 16:22:33 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>, mst@...hat.com,
        alex.williamson@...hat.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, dan.daly@...el.com
Subject: Re: [PATCH 3/7] vhost_vdpa: implement IRQ offloading functions in
 vhost_vdpa


On 2020/7/12 下午10:49, 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@...el.com>
> ---
>   drivers/vhost/vdpa.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 69 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 2fcc422..92683e4 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -115,6 +115,63 @@ 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;
> +
> +	vq_err(vq, "setup irq bypass for vq %d with irq = %d\n", qid, irq);
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	if (!vq->call_ctx.ctx)
> +		return;
> +
> +	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);
> +
> +	if (unlikely(ret))
> +		vq_err(vq,
> +		"irq bypass producer (token %p registration fails: %d\n",
> +		vq->call_ctx.producer.token, ret);


Not sure this deserves a vq_err(), irq will be relayed through eventfd 
if irq bypass manager can't work.


> +}
> +
> +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);
> +
> +	vq_err(vq, "unsetup irq bypass for vq %d\n", qid);


Why call vq_err() here?


> +}
> +
> +static void vhost_vdpa_update_vq_irq(struct vhost_virtqueue *vq)
> +{
> +	struct eventfd_ctx *ctx;
> +	void *token;
> +
> +	spin_lock(&vq->call_ctx.ctx_lock);
> +	ctx = vq->call_ctx.ctx;
> +	token = vq->call_ctx.producer.token;
> +	if (ctx == token)
> +		return;


Need do unlock here.


> +
> +	if (!ctx && token)
> +		irq_bypass_unregister_producer(&vq->call_ctx.producer);
> +
> +	if (ctx && ctx != token) {
> +		irq_bypass_unregister_producer(&vq->call_ctx.producer);
> +		vq->call_ctx.producer.token = ctx;
> +		irq_bypass_register_producer(&vq->call_ctx.producer);
> +	}
> +
> +	spin_unlock(&vq->call_ctx.ctx_lock);


This should be rare so I'd use simple codes just do unregister and register.


> +}
> +
>   static void vhost_vdpa_reset(struct vhost_vdpa *v)
>   {
>   	struct vdpa_device *vdpa = v->vdpa;
> @@ -332,6 +389,7 @@ static long vhost_vdpa_set_config_call(struct vhost_vdpa *v, u32 __user *argp)
>   
>   	return 0;
>   }
> +


Unnecessary change.


>   static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>   				   void __user *argp)
>   {
> @@ -390,6 +448,16 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>   			cb.private = NULL;
>   		}
>   		ops->set_vq_cb(vdpa, idx, &cb);
> +#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
> +		/*
> +		 * 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);
> +#endif
>   		break;
>   
>   	case VHOST_SET_VRING_NUM:
> @@ -741,6 +809,7 @@ static int vhost_vdpa_open(struct inode *inode, struct file *filep)
>   		vqs[i] = &v->vqs[i];
>   		vqs[i]->handle_kick = handle_vq_kick;
>   	}
> +


Unnecessary change.

Thanks


>   	vhost_dev_init(dev, vqs, nvqs, 0, 0, 0, false,
>   		       vhost_vdpa_process_iotlb_msg);
>