On Tuesday, January 10, 2017 8:07:20 AM CET Christoph Hellwig wrote: > On Tue, Jan 10, 2017 at 09:47:21AM +0300, Nikita Yushchenko wrote: > > I'm now working with HW that: > > - is now way "low end" or "obsolete", it has 4G of RAM and 8 CPU cores, > > and is being manufactured and developed, > > - has 75% of it's RAM located beyond first 4G of address space, > > - can't physically handle incoming PCIe transactions addressed to memory > > beyond 4G. > > It might not be low end or obselete, but it's absolutely braindead. > Your I/O performance will suffer badly for the life of the platform > because someone tries to save 2 cents, and there is not much we can do > about it. Unfortunately it is a common problem for arm64 chips that were designed by taking a 32-bit SoC and replacing the CPU core. The swiotlb is the right workaround for this, and I think we all agree that we should just make it work correctly. Arnd
