netdev - Re: [PATCH V4 2/4] vDPA/ifcvf: implement device MSIX vector allocator

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Date:   Mon, 14 Feb 2022 14:26:02 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>, mst@...hat.com
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH V4 2/4] vDPA/ifcvf: implement device MSIX vector allocator


在 2022/2/3 下午3:27, Zhu Lingshan 写道:
> This commit implements a MSIX vector allocation helper
> for vqs and config interrupts.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> ---
>   drivers/vdpa/ifcvf/ifcvf_main.c | 35 +++++++++++++++++++++++++++++++--
>   1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c b/drivers/vdpa/ifcvf/ifcvf_main.c
> index d1a6b5ab543c..44c89ab0b6da 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
> @@ -58,14 +58,45 @@ static void ifcvf_free_irq(struct ifcvf_adapter *adapter, int queues)
>   	ifcvf_free_irq_vectors(pdev);
>   }
>   
> +/* ifcvf MSIX vectors allocator, this helper tries to allocate
> + * vectors for all virtqueues and the config interrupt.
> + * It returns the number of allocated vectors, negative
> + * return value when fails.
> + */
> +static int ifcvf_alloc_vectors(struct ifcvf_adapter *adapter)
> +{
> +	struct pci_dev *pdev = adapter->pdev;
> +	struct ifcvf_hw *vf = &adapter->vf;
> +	int max_intr, ret;
> +
> +	/* all queues and config interrupt  */
> +	max_intr = vf->nr_vring + 1;
> +	ret = pci_alloc_irq_vectors(pdev, 1, max_intr, PCI_IRQ_MSIX | PCI_IRQ_AFFINITY);
> +
> +	if (ret < 0) {
> +		IFCVF_ERR(pdev, "Failed to alloc IRQ vectors\n");
> +		return ret;
> +	}
> +
> +	if (ret < max_intr)
> +		IFCVF_INFO(pdev,
> +			   "Requested %u vectors, however only %u allocated, lower performance\n",
> +			   max_intr, ret);
> +
> +	return ret;
> +}
> +
>   static int ifcvf_request_irq(struct ifcvf_adapter *adapter)
>   {
>   	struct pci_dev *pdev = adapter->pdev;
>   	struct ifcvf_hw *vf = &adapter->vf;
> -	int vector, i, ret, irq;
> +	int vector, nvectors, i, ret, irq;
>   	u16 max_intr;
>   
> -	/* all queues and config interrupt  */
> +	nvectors = ifcvf_alloc_vectors(adapter);
> +	if (!(nvectors > 0))
> +		return nvectors;


Why not simply checking by using nvectors <= 0? If ifcvf_alloc_vectors 
can return 0 this breaks the ifcvf_request_irq() caller's assumption.


> +
>   	max_intr = vf->nr_vring + 1;
>   
>   	ret = pci_alloc_irq_vectors(pdev, max_intr,


So irq is allocated twice here?

Thanks