Re: MMIO and gcc re-ordering issue

Alan Cox
2008-06-04T11:47:14Z

> Anyway, Intel certainly seems to document that WC memory is serialized by
> any access to UC memory.

I don't believe that is actually true on Pentium Pro at least.

> So what started out as a "we can do accesses to the frame buffer more
> efficiently without anybody ever even having to know or care" has
> turned into a whole nightmare of people using it for other things, and
> then you very much _do_ have to care! ]

Notably graphics where 3Dfx lined the registers up specifically to make
this work. We were also using it with I²O where it gave a small
performance gain.

Alan