Le Wed, 30 Sep 2009 16:47:33 +1300,
Michal Ludvig <mludvig@xxxxxxxxxxxx> a écrit :
> I've got two questions:
> 1) Can I speed it up somehow?
> 2) Apparently it's quite a lot of time between calling outb() and its
> return. Can the kernel do something else in the meantime, like
> scheduling another process or handling interrupts, or is it blocked
> waiting for the outb() return? I'm on a uniprocessor x86 system.
You can read the implementation of outb() for x86
in /home/thomas/local/linuxdev/arch/x86/include/asm/io_32.h. Unless you
use outb_p() (which introduces a pause after the write), outb() is only
a static inline function that does the "outb" CPU instruction. No more,
no less.
If you want to be 100%, for testing purposes, you can hand-code the
outb() using an asm("") statement. But I don't think it'll make any
difference.
You can also make an accurate measurement of the instruction duration
using the TSC, to get the number of cycles spent during the execution
of the instruction.
Finally, my hardware knowledge is a bit limited, but I'm not sure that
a 8 Mhz bus necessarly means that you can do 8 millions outb() per
second through this bus. One outb() probably requires several (if not
many) clock ticks.
Sincerly,
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com
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