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Message-ID: <80272f12-aeb2-e4b2-013e-bedefa1f23e9@redhat.com>
Date: Wed, 5 Aug 2020 10:36:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Zhu, Lingshan" <lingshan.zhu@...el.com>,
alex.williamson@...hat.com, mst@...hat.com, pbonzini@...hat.com,
sean.j.christopherson@...el.com, wanpengli@...cent.com
Cc: 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 2020/8/4 下午5:31, 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,
This is not how the code is wrote? See above you only check whether irq
is negative, irq 0 seems acceptable.
+ 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);
> 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().
I'm not sure I get this but do you have a case for this?
> is it worth for simplify the code?
Less code(bug).
>>
>>> +
>>> 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!
>>
>>
>>> + 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,
But you check irq here? For ctx, irq_bypass_unregister_producer() can do
the check instead of us.
Thanks
> 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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