Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs

Will Deacon
2020-09-17T19:42:49Z

On Thu, Sep 17, 2020 at 03:01:16PM +0100, Lorenzo Pieralisi wrote:
> On Thu, Sep 17, 2020 at 08:32:21AM -0300, Jason Gunthorpe wrote:
> > On Thu, Sep 17, 2020 at 11:28:19AM +0100, Lorenzo Pieralisi wrote:
> > > Unfortunately if we merge this patch we _do_ know from this thread
> > > that userspace will suffer from a perf regression on TX2.
> > >
> > > Either we ignore it or we write some code to prevent it
> > > (ie first step make arch_can_pci_mmap_wc() return 0 on TX2 -
> > > possibly using the arm64 errata detection mechanism).
> >
> > If anyone complains they can send the change to arch_can_pci_mmap_wc()
> > - I'm pretty sure nobody will complain due to mlx5
>
> If that's the case we can go ahead and merge this patch with a
> reworded commit log - this thread was very useful nonetheless
> for my own information (and others hopefully) so thank you.
>
> For VFIO WC + "message push ioremap" - to be continued.
>
> Clint, please reword the commit and resend, not sure we can hit
> v5.10 but we shall try.

If you ack it, I'll queue it ;)

Will