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

[Zenghui Yu]

Hi Cornelia,

On 2020/9/21 18:21, Cornelia Huck wrote:
> On Mon, 21 Sep 2020 12:51:16 +0800
> Zenghui Yu <yuzenghui@xxxxxxxxxx> 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." ?

Yes.

> > Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > ---
> > * 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@xxxxxxxxxx>

Thanks for you review! I think Alex can help fix the commit message when
applying? Otherwise I can send a v3.


Thanks,
Zenghui