Resource sem issue
mantegazza at aero.polimi.it
Thu Oct 28 17:08:11 CEST 2004
Steven Seeger wrote:
> I've never used LXRT before. What would I do differently? I thought LXRT was
> doing more scheduling stuff from user space or something.
Once more! LXRT can schedule kernel only applications also. It can do so
by using Linux kernel threads or RTAI proper tasks. The choice is set by
setting its macro USE_RTAI_TASKS to 0/1. The default that comes with the
distribution is 0 (do not use), because RTAI proper tasks have not been
tested well in mixed user/kernel mode. The difference in performance
between the two mode is just that you have to pay a bit more overhead,
in the latter case. Such a overhead is negligible with respect to the
architectural jitter, at least on ix86.
I already informed RTAI users that, better sooner than later, they will
be using just LXRT, even if they insmod rtai_up. The reasons are:
- for more than 2 years nobody has used anything but LXRT here at DIAPM
- performancewise there is just the illusion of better performances, as
said above. At DIAPM we have been likely the only ones to run latency
calibration in parallel with real lasting applications. The result is
that, given enough running time, sched_up has the same worst case than LXRT
- so it is simpler to maintain just one thing.
Clearly there is the problem of making LXRT architecture indifferent.
That is not the same as having user space support for real time and can
be done quite easily. It is just a matter of finding somebody with the
good will to interoperate with me on a non ix86 architecture, to make
LXRT nomore ix86 specific anywhere, it is close to that already.
In your case the behaviour will be likely the same but I asked you to do
so because I'm willing to care of just LXRT.
More information about the Rtai