Re: [PATCH 2/3] x86_64: Define 128-bit memory-mapped I/O operations

On Wed, Aug 22, 2012 at 7:50 AM, Linus Torvalds
[off-list ref] wrote:

But I got google to find it for me by looking for "__raw_writeo", so I
can see the patch now. It looks like it might work. Does it really
help performance despite always doing those TS games in CR0 for each
access?

Btw, are we even certain that a 128-bit PCIe write is going to remain
atomic across a bus (ie over various PCIe bridges etc)? Do you you
care? Is it just a "one transaction is cheaper than two", and it
doesn't really have any ordering constraints? If the thing gets split
into two 64-bit transactions (in whatever order) by a bridge on the
way, would that be ok?

We've seen buses split accesses before (ie 64-bit writes on 32-bit PCI).

                     Linus