Re: [PATCH v2 2/2] vfio/pci: Don't regenerate vconfig for all BARs if !bardirty

Cornelia Huck
2020-09-21T10:21:52Z

On Mon, 21 Sep 2020 12:51:16 +0800
Zenghui Yu <yuzenghui@huawei.com> wrote:

> Now we regenerate vconfig for all the BARs via vfio_bar_fixup(), every time
> any offset of any of them are read. Though BARs aren't re-read regularly,
> the regeneration can be avoid if no BARs had been written since they were

s/avoid/avoided/

> last read, in which case the vdev->bardirty is false.

s/the//

>
> Let's predicate the vfio_bar_fixup() on the bardirty so that it can return
> immediately if !bardirty.

Maybe

"Let's return immediately in vfio_bar_fixup() if bardirty is false." ?

>
> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
> * From v1:
> - Per Alex's suggestion, let vfio_bar_fixup() test vdev->bardirty to
> avoid doing work if bardirty is false, instead of removing it entirely.
> - Rewrite the commit message.
>
> drivers/vfio/pci/vfio_pci_config.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index d98843feddce..5e02ba07e8e8 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -467,6 +467,9 @@ static void vfio_bar_fixup(struct vfio_pci_device *vdev)
> __le32 *vbar;
> u64 mask;
>
> + if (!vdev->bardirty)

Finally, bardirty can actually affect something :)

> + return;
> +
> vbar = (__le32 *)&vdev->vconfig[PCI_BASE_ADDRESS_0];
>
> for (i = 0; i < PCI_STD_NUM_BARS; i++, vbar++) {

Reviewed-by: Cornelia Huck <cohuck@redhat.com>