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

Gavin Liu
2024-04-22T10:59:24Z

Dear Michael,

I hope this email finds you well. I am reaching out to request your assistance in reviewing a patch.

The patch in question is titled "[PATCH v5] vp_vdpa: don't allocate unused msix vectors". I believe your expertise and insights would be invaluable in ensuring the quality and effectiveness of this patch.

Your feedback and review are highly appreciated. Please let me know if you have any questions or require further information.

Thank you for your time and consideration.

Best regards,
Yuxue Liu

-----Original Message-----
From: Gavin Liu
Sent: April 10, 2024 11:31
To: mst@redhat.com; jasowang@redhat.com
Cc: Angus Chen angus.chen@jaguarmicro.com; virtualization@lists.linux.dev; xuanzhuo@linux.alibaba.com; Gavin Liu gavin.liu@jaguarmicro.com; linux-kernel@vger.kernel.org; Heng Qi hengqi@linux.alibaba.com
Subject: [PATCH v5] vp_vdpa: don't allocate unused msix vectors
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. 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@jaguarmicro.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