Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

Andi Kleen
2007-12-11T16:30:29Z

> Most, probably most-all, of the delays to port operations
> on modern ix86 machines are not needed at all. Certainly

We know this. The problem is that there is no good known way to
figure out which machines need it. Also it is typically
slow hardware anyways -- the most time critical is probably
the 8259, but nobody who cares about performance still uses
it except as a fail safe fallback and for those it is better
to be conservative.

> machines that use bridges to expand port I/O to the ISA
> bus do need any such delays. There are exactly two (and

It has been observed to be required talking to some older
PCI based northbridges too.

> (2) I/O operations that have two ports, one an index
> port and the other a data port, like the CMOS RTC. Once

and PIT etc.

Anyways it looks like the discussion here is going in a
a loop. I had hoped David would post his test results with
another port so that we know for sure that the bus aborts
(and not port 80) is the problem on his box. But it looks like
he doesn't want to do this. Still removing the bus aborts
is probably the correct way to go forward.

Only needs a patch now. If nobody beats me to it i'll
add one later to my tree.

-Andi