ACK/Cmnt: [SRU][AWS-{B,F,G}] enable PCI write-combine for arm64

[Andrea Righi]

On Wed, Sep 02, 2020 at 07:50:16AM -0700, Kamal Mostafa wrote:
> BugLink: https://bugs.launchpad.net/bugs/1893817
> 
> To improve PCI performance on arm64 AWS instances, enable arch_can_pci_mmap_wc()
> via the patch:
> 
>   From: Clint Sbisa <csbisa at amazon.com>
>   Subject: [PATCH] arm64: Enable PCI write-combine resources under sysfs
> 
>   https://lore.kernel.org/linux-pci/20200831151827.pumm2p54fyj7fz5s@amazon.com/
> 
> 
> Supplied here are two versions of this one-liner patch:
>     [PATCH][AWS-B]       <--  for linux-aws/bionic master (v4.15)
>     [PATCH][AWS-{F,G}]   <--  for linux-aws/{focal and groovy} master
> 
> I have smoke-tested this on AWS ARM instances.

After reading the upstream thread it seems that there are still some
concerns about this patch (potential side effects with other drivers on
arm64). It'd be nice to know if it actually improves performance (I
couldn't find any numbers / benchmark results in the original email
thread, but I'm assuming it has been tested/measured).

And if we apply this patch it'd be nice to follow the development of
this work, if a new version comes out we may need to revert this and
apply the new one.

Under these assumptions:

Acked-by: Andrea Righi <andrea.righi at canonical.com>

-Andrea