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Date: Tue, 4 Aug 2020 05:36:22 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: "Zhu, Lingshan" <lingshan.zhu@...el.com>
Cc: Jason Wang <jasowang@...hat.com>, alex.williamson@...hat.com,
pbonzini@...hat.com, sean.j.christopherson@...el.com,
wanpengli@...cent.com, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, kvm@...r.kernel.org, eli@...lanox.com,
shahafs@...lanox.com, parav@...lanox.com
Subject: Re: [PATCH V5 4/6] vhost_vdpa: implement IRQ offloading in vhost_vdpa
On Tue, Aug 04, 2020 at 05:31:38PM +0800, Zhu, Lingshan wrote:
>
> On 8/4/2020 4:51 PM, Jason Wang wrote:
>
>
> On 2020/7/31 下午2:55, 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.
>
> With these functions, this commit can setup/unsetup
> irq offloading through setting DRIVER_OK/!DRIVER_OK, and
> update irq offloading through SET_VRING_CALL.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> Suggested-by: Jason Wang <jasowang@...hat.com>
> ---
> drivers/vhost/Kconfig | 1 +
> drivers/vhost/vdpa.c | 79
> ++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 79 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index d3688c6afb87..587fbae06182 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 df3cf386b0cd..278ea2f00172 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -115,6 +115,55 @@ static irqreturn_t vhost_vdpa_config_cb(void
> *private)
> return IRQ_HANDLED;
> }
> +static void vhost_vdpa_setup_vq_irq(struct vhost_vdpa *v, u16 qid)
> +{
> + struct vhost_virtqueue *vq = &v->vqs[qid];
> + const struct vdpa_config_ops *ops = v->vdpa->config;
> + struct vdpa_device *vdpa = v->vdpa;
> + int ret, irq;
> +
> + spin_lock(&vq->call_ctx.ctx_lock);
> + irq = ops->get_vq_irq(vdpa, qid);
> + if (!vq->call_ctx.ctx || irq < 0) {
> + spin_unlock(&vq->call_ctx.ctx_lock);
> + 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);
> +}
> +
> +static void vhost_vdpa_unsetup_vq_irq(struct vhost_vdpa *v, u16 qid)
> +{
> + struct vhost_virtqueue *vq = &v->vqs[qid];
> +
> + spin_lock(&vq->call_ctx.ctx_lock);
> + irq_bypass_unregister_producer(&vq->call_ctx.producer);
>
>
>
> Any reason for not checking vq->call_ctx.producer.irq as below here?
>
> we only need ctx as a token to unregister vq from irq bypass manager, if vq->call_ctx.producer.irq is 0, means it is a unused or disabled vq, no harm if we
> perform an unregister on it.
>
>
>
> + 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);
> + /*
> + * 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) {
> + spin_unlock(&vq->call_ctx.ctx_lock);
> + return;
> + }
> +
> + 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);
> +}
>
>
>
> I think setup_irq() and update_irq() could be unified with the following
> logic:
>
> irq_bypass_unregister_producer(&vq->call_ctx.producer);
> irq = ops->get_vq_irq(vdpa, qid);
> if (!vq->call_ctx.ctx || irq < 0) {
> spin_unlock(&vq->call_ctx.ctx_lock);
> 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);
>
> Yes, this code piece can do both register and update. Though it's rare to call undate_irq(), however
> setup_irq() is very likely to be called for every vq, so this may cause several rounds of useless irq_bypass_unregister_producer().
> is it worth for simplify the code?
>
>
> +
> static void vhost_vdpa_reset(struct vhost_vdpa *v)
> {
> struct vdpa_device *vdpa = v->vdpa;
> @@ -155,11 +204,15 @@ static long vhost_vdpa_set_status(struct
> vhost_vdpa *v, u8 __user *statusp)
> {
> struct vdpa_device *vdpa = v->vdpa;
> const struct vdpa_config_ops *ops = vdpa->config;
> - u8 status;
> + u8 status, status_old;
> + int nvqs = v->nvqs;
> + u16 i;
> if (copy_from_user(&status, statusp, sizeof(status)))
> return -EFAULT;
> + status_old = ops->get_status(vdpa);
> +
> /*
> * Userspace shouldn't remove status bits unless reset the
> * status to 0.
> @@ -169,6 +222,15 @@ static long vhost_vdpa_set_status(struct
> vhost_vdpa *v, u8 __user *statusp)
> ops->set_status(vdpa, status);
> + /* vq irq is not expected to be changed once DRIVER_OK is set */
>
>
>
> Let's move this comment to the get_vq_irq bus operation.
>
> OK, can do!
>
>
Patch on top pls, these are in my tree now.
>
> + if ((status & VIRTIO_CONFIG_S_DRIVER_OK) && !(status_old &
> VIRTIO_CONFIG_S_DRIVER_OK))
> + for (i = 0; i < nvqs; i++)
> + vhost_vdpa_setup_vq_irq(v, i);
> +
> + if ((status_old & VIRTIO_CONFIG_S_DRIVER_OK) && !(status &
> VIRTIO_CONFIG_S_DRIVER_OK))
> + for (i = 0; i < nvqs; i++)
> + vhost_vdpa_unsetup_vq_irq(v, i);
> +
> return 0;
> }
> @@ -332,6 +394,7 @@ static long vhost_vdpa_set_config_call(struct
> vhost_vdpa *v, u32 __user *argp)
> return 0;
> }
> +
> static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int
> cmd,
> void __user *argp)
> {
> @@ -390,6 +453,7 @@ static long vhost_vdpa_vring_ioctl(struct
> vhost_vdpa *v, unsigned int cmd,
> cb.private = NULL;
> }
> ops->set_vq_cb(vdpa, idx, &cb);
> + vhost_vdpa_update_vq_irq(vq);
> break;
> case VHOST_SET_VRING_NUM:
> @@ -765,6 +829,18 @@ static int vhost_vdpa_open(struct inode *inode,
> struct file *filep)
> return r;
> }
> +static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)
> +{
> + struct vhost_virtqueue *vq;
> + int i;
> +
> + for (i = 0; i < v->nvqs; i++) {
> + vq = &v->vqs[i];
> + if (vq->call_ctx.producer.irq)
> + irq_bypass_unregister_producer(&vq->call_ctx.producer);
> + }
> +}
>
>
>
> Why not using vhost_vdpa_unsetup_vq_irq()?
>
> IMHO, in this cleanup phase, the device is almost dead, user space won't change ctx anymore, so I think we don't need to check ctx or irq, can just unregister it.
>
> Thanks!
>
>
> Thanks
>
>
>
> +
> static int vhost_vdpa_release(struct inode *inode, struct file
> *filep)
> {
> struct vhost_vdpa *v = filep->private_data;
> @@ -777,6 +853,7 @@ static int vhost_vdpa_release(struct inode *inode,
> struct file *filep)
> vhost_vdpa_iotlb_free(v);
> vhost_vdpa_free_domain(v);
> vhost_vdpa_config_put(v);
> + vhost_vdpa_clean_irq(v);
> vhost_dev_cleanup(&v->vdev);
> kfree(v->vdev.vqs);
> mutex_unlock(&d->mutex);
>
>
>
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