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

Lorenzo Pieralisi
2020-09-16T21:03:07Z

On Wed, Sep 16, 2020 at 09:12:26AM -0300, Jason Gunthorpe wrote:

[...]

> > You mean the driver uses a different path to the HW which ahs that
> > overhead, not that MMIOs have that overhead right ?
>
> The different path has overhead of doing extra useless MMIOs because
> they don't combine

For my own information, this is IB user space driver code, correct ? It
tries to mmap buffer as WC and if it succeeds write into it in an
optimized fashion (that is just pure overhead on platforms where normal
NC memory - ie WC on arm64 - does not do what the _architecture_ defines
it should).

Lorenzo