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

[linux@horizon.com]

Here are a variety of machines:

600 MHz PIII (Katmai), 440BX chipset, 82371AB/EB/MB PIIX4 ISA bridge:
cycles: out 794, in 348
cycles: out 791, in 348
cycles: out 791, in 349
cycles: out 791, in 348
cycles: out 791, in 348

433 MHz Celeron (Mendocino), 440 BX chipset, same ISA bridge:
cycles: out 624, in 297
cycles: out 623, in 296
cycles: out 624, in 297
cycles: out 623, in 297
cycles: out 623, in 296

1100 MHz Athlon, nForce2 chipset, nForce2 ISA bridge:
cycles: out 1295, in 1162
cycles: out 1295, in 1162
cycles: out 1295, in 1162
cycles: out 1295, in 1162
cycles: out 1295, in 1162

800 MHz Transmeta Crusoe TM5800, Transmeta/ALi M7101 chipset.
cycles: out 1212, in 388
cycles: out 1195, in 375
cycles: out 1197, in 377
cycles: out 1196, in 376
cycles: out 1196, in 377

2200 MHz Athlon 64, K8T890 chipset, VT8237 ISA bridge:
cycles: out 1844674407370814, in 1844674407365758
cycles: out 1844674407370813, in 1844674407365756
cycles: out 1844674407370805, in 1844674407365750
cycles: out 1844674407370813, in 1844674407365755
cycles: out 1844674407370814, in 1844674407365756

Um, huh?  That's gcc 4.2.3 (Debian version 4.2.2-4), -O2.  Very odd.

I can run it with -O0:
cycles: out 4894, in 4894
cycles: out 4905, in 4917
cycles: out 4910, in 4896
cycles: out 4909, in 4896
cycles: out 4894, in 4898
cycles: out 4911, in 4898

or with -O2 -m32:
cycles: out 4914, in 4927
cycles: out 4913, in 4927
cycles: out 4913, in 4913
cycles: out 4914, in 4913
cycles: out 4913, in 4929
cycles: out 4912, in 4912
cycles: out 4913, in 4915

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