Re: [PATCH v3 8/9] Revert "vfio: Avoid disabling and enabling vectors repeatedly in VFIO migration"

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 21 Sep 2021 07:02:01 +0800
"Longpeng(Mike)" <longpeng2@huawei.com> wrote:

> Commit ecebe53fe993 ("vfio: Avoid disabling and enabling vectors
> repeatedly in VFIO migration") avoid inefficiently disabling and

s/avoid/avoids/

> enabling vectors repeatedly and let the unmasked vectors to be

s/let/lets/  s/to//

> enabled one by one.
> 
> But we want to batch multiple routes and defer the commit, and only
> commit once out side the loop of setting vector notifiers, so we

s/out side/outside/

> cannot to enable the vectors one by one in the loop now.

s/to//

Thanks,
Alex

> 
> Revert that commit and we will take another way in the next patch,
> it can not only avoid disabling/enabling vectors repeatedly, but
> also satisfy our requirement of defer to commit.
> 
> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
> ---
>  hw/vfio/pci.c | 20 +++-----------------
>  1 file changed, 3 insertions(+), 17 deletions(-)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 8fe238b11d..2de1cc5425 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -610,9 +610,6 @@ static __attribute__((unused)) void vfio_commit_kvm_msi_virq(VFIOPCIDevice *vdev
>  
>  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);
> @@ -631,22 +628,11 @@ 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.
>       */
> -    if (!pdev->msix_function_masked) {
> -        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);
> +    vfio_msix_vector_do_use(&vdev->pdev, 0, NULL, NULL);
> +    vfio_msix_vector_release(&vdev->pdev, 0);
>  
> -    if (msix_set_vector_notifiers(pdev, vfio_msix_vector_use,
> +    if (msix_set_vector_notifiers(&vdev->pdev, vfio_msix_vector_use,
>                                    vfio_msix_vector_release, NULL)) {
>          error_report("vfio: msix_set_vector_notifiers failed");
>      }