Michel Doyon wrote:
>
> Hi,
>
> I have been performing some timings with the semaphores under RTAI.
> I have a DUAL P-III 500 Mhz.
>
> I find a 9 usec time between the moment a semaphore is released on one CPU
> and the time a task on the other CPU is started. The initial semaphore
> release is done by a user put to the rt fifo and the fifo handler make
> the real call.
>
> On the other hand, I find that with a interrupt handler, releasing a
> semaphore to say task 1 running on the same CPU, it takes roughly the same
> time (10 usec) but if the task is set to run on a different cpu, than the
> irq hanbdler, it takes up to 16 usec.
>
> Do these number make sense ? I run the scheduler for SMP and rtai 0.9a
> with kernel 13 of linux.
>
> I took my measurements using a outb to the paralle port.
>
> Any comments or suggestions to speed this up ? I have been told that
> Windows NT is around 5 usec ... BUT I have not seen it myself nor have
> details on the timing measurement system.
Hi Michael,
See Paolo's answer as to why, but one thing I'd like to add is the
figures are quite reasonable. Remember that to make the measurement,
you are writing to the parallel port through the ISA bus, and this alone
can introduce several microseconds delays. I suspect the NT figures you
quote would for instance remove this overhead in their calculation. To
the largest extent, the performance is limited by hardware and
architecture rather than software.
Regards, Stuart
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