Re: [RFT] Port 0x80 I/O speed

[Rene Herman]

On 12-12-07 12:20, linux@xxxxxxxxxxx wrote:

> Here are a variety of machines:

Thanks much for all! Collecting all data now...

> With -O2, the cycle counts come out (before division) as
> out: 0xFFFFFFFFFFEA6F4F
> in:  0xFFFFFFFFFCE68BB6
> I think the "A" constraint doesn't work quite the same in
> 64-bit code.  The compiler seems to be using %rdx rather than
> %edx:%eax.

Yes indeed, that tripped me up. Have been using the "=A" locally for a while 
for similar timing tests. Will use a manual "=a" (lo), "=d" (hi) I guess for 
amd64 compatibility from now on.

If I'd care deeply I'd probably categorize this as a backwards compatibility 
bug in GCC though. Things were probably never guaranteed but they certainly 
worked that way...

Rene.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/