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

Gavin Liu
2024-04-26T03:12:45Z

Hi mst.

> > > >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?

>Not really. Guest disables interrupts presumably (it's polling) why does device still send them?

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

1：The guest os uses PMD mode, so the guest os won't receive interrupts. We can reach a consensus on this point.

2：Note that the MSIX interrupts mentioned here refer to the interrupts received by PCI devices on the host from the hardware.

3：In the guest OS, Virtio devices use PMD mode. The host does not need to enable the MSIX capability of the PCI device,
nor does it need to register interrupt callbacks. Do you agree with this?

4: Note that the patch is proposed to ensure that PCI devices on the host are not disturbed by interrupts.

----- Forwarded Message -----
From: Michael S. Tsirkin mst@redhat.com
Sent: April 26, 2024 6:10 AM
To: Angus Chen angus.chen@jaguarmicro.com
Cc: Gavin Liu gavin.liu@jaguarmicro.com; jasowang@redhat.com; virtualization@lists.linux.dev; xuanzhuo@linux.alibaba.com; linux-kernel@vger.kernel.org; Heng Qi hengqi@linux.alibaba.com
Subject: Re: Reply: [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 Tue, Apr 23, 2024 at 08:42:57AM +0000, Angus Chen wrote:
> Hi mst.
>
> > -----Original Message-----
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Tuesday, April 23, 2024 4:35 PM
> > 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: 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@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
> > >
> >
> > 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?

Not really. Guest disables interrupts presumably (it's polling) why does device still send them?

> >
> > >
> > >
> > > ----- 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
> > >
> > >
> > >
> > > 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@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@jagu
> > > > armicr
> > > > 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
> > >
>