Alan Cox [off-list ref] writes:

On Wed, 2002-09-18 at 18:27, Eric W. Biederman wrote:

quoted

Plus I have played with calibrating the TSC with outb to port
0x80 and there was enough variation that it was unuseable.  On some
newer systems it would take twice as long as on some older ones.

port 0x80 isnt going to PCI space.

Agreed.  It isn't going anywhere, and it takes it a while to recogonize
that.
 

x86 generally posts mmio write but not io write. Thats quite measurable.

The difference timing difference between posted and non-posted writes
I can see.

Eric