回复: [PATCH v5] vp_vdpa: don't allocate unused msix vectors

Gavin Liu
2024-04-23T01:39:22Z

On Wed, Apr 10, 2024 at 11:30:20AM +0800, lyx634449800 wrote:
> From: Yuxue Liu <yuxue.liu@jaguarmicro.com>
>
> When there is a ctlq and it doesn't require interrupt callbacks,the
> original method of calculating vectors wastes hardware msi or msix
> resources as well as system IRQ resources.
>
> When conducting performance testing using testpmd in the guest os, it
> was found that the performance was lower compared to directly using
> vfio-pci to passthrough the device
>
> In scenarios where the virtio device in the guest os does not utilize
> interrupts, the vdpa driver still configures the hardware's msix
> vector. Therefore, the hardware still sends interrupts to the host os.

>I just have a question on this part. How come hardware sends interrupts does not guest driver disable them?

1：Assuming the guest OS's Virtio device is using PMD mode, QEMU sets the call fd to -1
2：On the host side, the vhost_vdpa program will set vp_vdpa->vring[i].cb.callback to invalid
3：Before the modification, the vp_vdpa_request_irq function does not check whether
vp_vdpa->vring[i].cb.callback is valid. Instead, it enables the hardware's MSIX
interrupts based on the number of queues of the device

----- Original Message -----
From: Michael S. Tsirkin mst@redhat.com
Sent: April 22, 2024 20:09
To: Gavin Liu gavin.liu@jaguarmicro.com
Cc: jasowang@redhat.com; Angus Chen angus.chen@jaguarmicro.com; virtualization@lists.linux.dev; xuanzhuo@linux.alibaba.com; linux-kernel@vger.kernel.org; Heng Qi hengqi@linux.alibaba.com
Subject: Re: [PATCH v5] vp_vdpa: don't allocate unused msix vectors

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On Wed, Apr 10, 2024 at 11:30:20AM +0800, lyx634449800 wrote:
> From: Yuxue Liu <yuxue.liu@jaguarmicro.com>
>
> When there is a ctlq and it doesn't require interrupt callbacks,the
> original method of calculating vectors wastes hardware msi or msix
> resources as well as system IRQ resources.
>
> When conducting performance testing using testpmd in the guest os, it
> was found that the performance was lower compared to directly using
> vfio-pci to passthrough the device
>
> In scenarios where the virtio device in the guest os does not utilize
> interrupts, the vdpa driver still configures the hardware's msix
> vector. Therefore, the hardware still sends interrupts to the host os.

I just have a question on this part. How come hardware sends interrupts does not guest driver disable them?

> Because of this unnecessary
> action by the hardware, hardware performance decreases, and it also
> affects the performance of the host os.
>
> Before modification:(interrupt mode)
> 32: 0 0 0 0 PCI-MSI 32768-edge vp-vdpa[0000:00:02.0]-0
> 33: 0 0 0 0 PCI-MSI 32769-edge vp-vdpa[0000:00:02.0]-1
> 34: 0 0 0 0 PCI-MSI 32770-edge vp-vdpa[0000:00:02.0]-2
> 35: 0 0 0 0 PCI-MSI 32771-edge vp-vdpa[0000:00:02.0]-config
>
> After modification:(interrupt mode)
> 32: 0 0 1 7 PCI-MSI 32768-edge vp-vdpa[0000:00:02.0]-0
> 33: 36 0 3 0 PCI-MSI 32769-edge vp-vdpa[0000:00:02.0]-1
> 34: 0 0 0 0 PCI-MSI 32770-edge vp-vdpa[0000:00:02.0]-config
>
> Before modification:(virtio pmd mode for guest os)
> 32: 0 0 0 0 PCI-MSI 32768-edge vp-vdpa[0000:00:02.0]-0
> 33: 0 0 0 0 PCI-MSI 32769-edge vp-vdpa[0000:00:02.0]-1
> 34: 0 0 0 0 PCI-MSI 32770-edge vp-vdpa[0000:00:02.0]-2
> 35: 0 0 0 0 PCI-MSI 32771-edge vp-vdpa[0000:00:02.0]-config
>
> After modification:(virtio pmd mode for guest os)
> 32: 0 0 0 0 PCI-MSI 32768-edge vp-vdpa[0000:00:02.0]-config
>
> To verify the use of the virtio PMD mode in the guest operating
> system, the following patch needs to be applied to QEMU:
> https://lore.kernel.org/all/20240408073311.2049-1-yuxue.liu@jaguarmicr
> o.com
>
> Signed-off-by: Yuxue Liu <yuxue.liu@jaguarmicro.com>
> Acked-by: Jason Wang <jasowang@redhat.com>
> Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
> ---
> V5: modify the description of the printout when an exception occurs
> V4: update the title and assign values to uninitialized variables
> V3: delete unused variables and add validation records
> V2: fix when allocating IRQs, scan all queues
>
> drivers/vdpa/virtio_pci/vp_vdpa.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c
> b/drivers/vdpa/virtio_pci/vp_vdpa.c
> index df5f4a3bccb5..8de0224e9ec2 100644
> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> @@ -160,7 +160,13 @@ static int vp_vdpa_request_irq(struct vp_vdpa *vp_vdpa)
> struct pci_dev *pdev = mdev->pci_dev;
> int i, ret, irq;
> int queues = vp_vdpa->queues;
> - int vectors = queues + 1;
> + int vectors = 1;
> + int msix_vec = 0;
> +
> + for (i = 0; i < queues; i++) {
> + if (vp_vdpa->vring[i].cb.callback)
> + vectors++;
> + }
>
> ret = pci_alloc_irq_vectors(pdev, vectors, vectors, PCI_IRQ_MSIX);
> if (ret != vectors) {
> @@ -173,9 +179,12 @@ static int vp_vdpa_request_irq(struct vp_vdpa *vp_vdpa)
> vp_vdpa->vectors = vectors;
>
> for (i = 0; i < queues; i++) {
> + if (!vp_vdpa->vring[i].cb.callback)
> + continue;
> +
> snprintf(vp_vdpa->vring[i].msix_name, VP_VDPA_NAME_SIZE,
> "vp-vdpa[%s]-%d\n", pci_name(pdev), i);
> - irq = pci_irq_vector(pdev, i);
> + irq = pci_irq_vector(pdev, msix_vec);
> ret = devm_request_irq(&pdev->dev, irq,
> vp_vdpa_vq_handler,
> 0, vp_vdpa->vring[i].msix_name,
> @@ -185,21 +194,22 @@ static int vp_vdpa_request_irq(struct vp_vdpa *vp_vdpa)
> "vp_vdpa: fail to request irq for vq %d\n", i);
> goto err;
> }
> - vp_modern_queue_vector(mdev, i, i);
> + vp_modern_queue_vector(mdev, i, msix_vec);
> vp_vdpa->vring[i].irq = irq;
> + msix_vec++;
> }
>
> snprintf(vp_vdpa->msix_name, VP_VDPA_NAME_SIZE, "vp-vdpa[%s]-config\n",
> pci_name(pdev));
> - irq = pci_irq_vector(pdev, queues);
> + irq = pci_irq_vector(pdev, msix_vec);
> ret = devm_request_irq(&pdev->dev, irq, vp_vdpa_config_handler, 0,
> vp_vdpa->msix_name, vp_vdpa);
> if (ret) {
> dev_err(&pdev->dev,
> - "vp_vdpa: fail to request irq for vq %d\n", i);
> + "vp_vdpa: fail to request irq for config: %d\n",
> + ret);
> goto err;
> }
> - vp_modern_config_vector(mdev, queues);
> + vp_modern_config_vector(mdev, msix_vec);
> vp_vdpa->config_irq = irq;
>
> return 0;
> --
> 2.43.0