> > 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
>
> So MSIX is enabled but why would it trigger? virtio PMD in poll mode presumably suppresses interrupts after all.
I didn't express the test model clearly. The testing model is as follows:
----testpmd---- ----testpmd---
^ ^
| |
| |
| |
v v
----vfio pci--- ---vfio pci---
----pci device --- --pci device--
----guest os ----- ----guest os ------
---virtio device-- ---vfio device--
------qemu------- ------qemu-------
^ ^
| |
| |
| |
v v
----vhost_vdpa---- ----vfio pci----
------------------------host os--------------------------
----------------------hw----------------------------
VF1 VF2
After the hardware completes DMA, it will still send an interrupt to the host OS.
-----Original Message-----
From: Angus Chen angus.chen@xxxxxxxxxxxxxxx
Sent: April 23, 2024 16:43
To: Michael S. Tsirkin mst@xxxxxxxxxx; Gavin Liu gavin.liu@xxxxxxxxxxxxxxx
Cc: jasowang@xxxxxxxxxx; virtualization@xxxxxxxxxxxxxxx; xuanzhuo@xxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Heng Qi hengqi@xxxxxxxxxxxxxxxxx
Subject: RE: Reply: [PATCH v5] vp_vdpa: don't allocate unused msix vectors
Hi mst.
> -----Original Message-----
> From: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Sent: Tuesday, April 23, 2024 4:35 PM
> To: Gavin Liu <gavin.liu@xxxxxxxxxxxxxxx>
> Cc: jasowang@xxxxxxxxxx; Angus Chen <angus.chen@xxxxxxxxxxxxxxx>;
> virtualization@xxxxxxxxxxxxxxx; xuanzhuo@xxxxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> Subject: Re: 回复: [PATCH v5] vp_vdpa: don't allocate unused msix
> vectors
>
> On Tue, Apr 23, 2024 at 01:39:17AM +0000, Gavin Liu wrote:
> > On Wed, Apr 10, 2024 at 11:30:20AM +0800, lyx634449800 wrote:
> > > From: Yuxue Liu <yuxue.liu@xxxxxxxxxxxxxxx>
> > >
> > > 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
> >
>
> So MSIX is enabled but why would it trigger? virtio PMD in poll mode
> presumably suppresses interrupts after all.
Virtio pmd is in the guest,but in host side,the msix is enabled,then the device will triger Interrupt normally. I analysed this bug before,and I think gavin is right.
Did I make it clear?
>
> >
> >
> > ----- Original Message -----
> > From: Michael S. Tsirkin mst@xxxxxxxxxx
> > Sent: April 22, 2024 20:09
> > To: Gavin Liu gavin.liu@xxxxxxxxxxxxxxx
> > Cc: jasowang@xxxxxxxxxx; Angus Chen angus.chen@xxxxxxxxxxxxxxx;
> virtualization@xxxxxxxxxxxxxxx; xuanzhuo@xxxxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Heng Qi hengqi@xxxxxxxxxxxxxxxxx
> > Subject: Re: [PATCH v5] vp_vdpa: don't allocate unused msix vectors
> >
> >
> >
> > External Mail: This email originated from OUTSIDE of the organization!
> > Do not click links, open attachments or provide ANY information
> > unless you
> recognize the sender and know the content is safe.
> >
> >
> > On Wed, Apr 10, 2024 at 11:30:20AM +0800, lyx634449800 wrote:
> > > From: Yuxue Liu <yuxue.liu@xxxxxxxxxxxxxxx>
> > >
> > > 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@jaguar
> > > micr
> > > o.com
> > >
> > > Signed-off-by: Yuxue Liu <yuxue.liu@xxxxxxxxxxxxxxx>
> > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > Reviewed-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> > > ---
> > > 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
> >
