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Tsirkin" To: Gavin Liu Cc: "jasowang@redhat.com" , Angus Chen , "virtualization@lists.linux.dev" , "xuanzhuo@linux.alibaba.com" , "linux-kernel@vger.kernel.org" , Heng Qi Subject: Re: =?utf-8?B?5Zue5aSN?= =?utf-8?Q?=3A?= [PATCH v5] vp_vdpa: don't allocate unused msix vectors Message-ID: <20240423043424-mutt-send-email-mst@kernel.org> References: <20240410033020.1310-1-yuxue.liu@jaguarmicro.com> <20240422080729-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 > > > > 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. > > > ----- 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 > > > > 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 > > Acked-by: Jason Wang > > Reviewed-by: Heng Qi > > --- > > 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 >