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

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Date:   Mon, 14 Feb 2022 14:46:37 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Jason Wang <jasowang@...hat.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



On 2/14/2022 2:26 PM, Jason Wang wrote:
>
> 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.
It can return zero if no vectors allocated, then ifcvf_request_irq 
fails. For sure I can use <=0

Thanks!
>
>
>> +
>>       max_intr = vf->nr_vring + 1;
>>         ret = pci_alloc_irq_vectors(pdev, max_intr,
>
>
> So irq is allocated twice here?
Oh, it is a rebasing problem, I should move the deleting line here from 
the next patch.

Thanks
>
> Thanks
>
>