Re: [PATCH v3 3/3] vfio: Avoid disabling and enabling vectors repeatedly in VFIO migration

[Alex Williamson]

On Tue, 9 Mar 2021 15:25:52 +0800
Shenming Lu <lushenming@huawei.com> wrote:

> On 2021/3/3 5:26, Alex Williamson wrote:
> > 
> > MST/Marcel,
> > 
> > Do you have an Ack or objection to exporting msix_masked() as below?  
> 
> Or could we use msix_function_masked instead as below? :-)
> 
> if (!pdev->msix_function_masked) {
>     for (nr = 0; nr < msix_nr_vectors_allocated(pdev); nr++) {
>         if (!msix_is_masked(pdev, nr)) {
>             max_vec = nr;
>         }
>     }
> }

Yeah, it looks like that should work.  I'll look for a v4 with that
change.  Thanks,

Alex

> > On Tue, 23 Feb 2021 10:22:25 +0800
> > Shenming Lu <lushenming@huawei.com> wrote:
> >   
> >> In VFIO migration resume phase and some guest startups, there are
> >> already unmasked vectors in the vector table when calling
> >> vfio_msix_enable(). So in order to avoid inefficiently disabling
> >> and enabling vectors repeatedly, let's allocate all needed vectors
> >> first and then enable these unmasked vectors one by one without
> >> disabling.
> >>
> >> Signed-off-by: Shenming Lu <lushenming@huawei.com>
> >> ---
> >>  hw/pci/msix.c         |  2 +-
> >>  hw/vfio/pci.c         | 20 +++++++++++++++++---
> >>  include/hw/pci/msix.h |  1 +
> >>  3 files changed, 19 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> >> index ae9331cd0b..e057958fcd 100644
> >> --- a/hw/pci/msix.c
> >> +++ b/hw/pci/msix.c
> >> @@ -131,7 +131,7 @@ static void msix_handle_mask_update(PCIDevice *dev, 
> >> int vector, bool was_masked)
> >>      }
> >>  }
> >>  
> >> -static bool msix_masked(PCIDevice *dev)
> >> +bool msix_masked(PCIDevice *dev)
> >>  {
> >>      return dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & 
> >> MSIX_MASKALL_MASK;
> >>  }
> >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >> index f74be78209..088fd41926 100644
> >> --- a/hw/vfio/pci.c
> >> +++ b/hw/vfio/pci.c
> >> @@ -569,6 +569,9 @@ static void vfio_msix_vector_release(PCIDevice *pdev, 
> >> unsigned int nr)
> >>  
> >>  static void vfio_msix_enable(VFIOPCIDevice *vdev)
> >>  {
> >> +    PCIDevice *pdev = &vdev->pdev;
> >> +    unsigned int nr, max_vec = 0;
> >> +
> >>      vfio_disable_interrupts(vdev);
> >>  
> >>      vdev->msi_vectors = g_new0(VFIOMSIVector, vdev->msix->entries);
> >> @@ -587,11 +590,22 @@ static void vfio_msix_enable(VFIOPCIDevice *vdev)
> >>       * triggering to userspace, then immediately release the vector, 
> >> leaving
> >>       * the physical device with no vectors enabled, but MSI-X enabled, 
> >> just
> >>       * like the guest view.
> >> +     * If there are already unmasked vectors (in migration resume phase 
> >> and
> >> +     * some guest startups) which will be enabled soon, we can allocate 
> >> all
> >> +     * of them here to avoid inefficiently disabling and enabling vectors
> >> +     * repeatedly later.
> >>       */
> >> -    vfio_msix_vector_do_use(&vdev->pdev, 0, NULL, NULL);
> >> -    vfio_msix_vector_release(&vdev->pdev, 0);
> >> +    if (!msix_masked(pdev)) {
> >> +        for (nr = 0; nr < msix_nr_vectors_allocated(pdev); nr++) {
> >> +            if (!msix_is_masked(pdev, nr)) {
> >> +                max_vec = nr;
> >> +            }
> >> +        }
> >> +    }
> >> +    vfio_msix_vector_do_use(pdev, max_vec, NULL, NULL);
> >> +    vfio_msix_vector_release(pdev, max_vec);
> >>  
> >> -    if (msix_set_vector_notifiers(&vdev->pdev, vfio_msix_vector_use,
> >> +    if (msix_set_vector_notifiers(pdev, vfio_msix_vector_use,
> >>                                    vfio_msix_vector_release, NULL)) {
> >>          error_report("vfio: msix_set_vector_notifiers failed");
> >>      }
> >> diff --git a/include/hw/pci/msix.h b/include/hw/pci/msix.h
> >> index 4c4a60c739..b3cd88e262 100644
> >> --- a/include/hw/pci/msix.h
> >> +++ b/include/hw/pci/msix.h
> >> @@ -28,6 +28,7 @@ void msix_load(PCIDevice *dev, QEMUFile *f);
> >>  
> >>  int msix_enabled(PCIDevice *dev);
> >>  int msix_present(PCIDevice *dev);
> >> +bool msix_masked(PCIDevice *dev);
> >>  
> >>  bool msix_is_masked(PCIDevice *dev, unsigned vector);
> >>  void msix_set_pending(PCIDevice *dev, unsigned vector);  
> > 
> > .
> >   
>