Date:   Wed, 5 Aug 2020 13:51:39 +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 2020/8/5 下午1:45, Zhu, Lingshan wrote:
>
>
> On 8/5/2020 10:36 AM, Jason Wang wrote:
>>
>> 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.
> Yes, IRQ 0 is valid, so we check whether it is < 0.
>>
>> +    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?
> I mean if we use this routine to setup irq offloading, it is very likely to do a unregister producer for every vq first, but for nothing.


Does it really harm? See vfio_msi_set_vector_signal()


>>
>>
>>> is it worth for simplify the code?
>>
>>
>> Less code(bug).
> I can do this if we are chasing for perfection, however I believe bug number has positive correlation with the complexity in the logic than code lines, if we only merge lines, this may not help.
>>

Well, reduce code duplication is always good and it helps for reviewers.


>>
>>>>
>>>>> +
>>>>>   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.
> IMHO, maybe irq does not matter, (1)if the vq not registered to irq bypass manager, producer.irq is not valid, token == NULL, irq_bypass_unregister would no nothing.
> (2)if the vq registered to irq bypass manager, producer.irq is valid, irq_bypass_unregister will do its work based on the token.
> so maybe we can say irq is relative to the token, we may don't need to check irq here.


So you agree to use vhost_vdpa_unsetup_vq_irq()?

Thanks


>
> Thanks!
>>
>> 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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