Re: [Xenomai] imx6q xenomai ipipe-3.0-imx6q

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Le 20/04/2014 07:06, eric a écrit :
> So if my program use lots of memory operations  for a long time it maybe
> gives non real-time activities opportunity to thrash the cache?

It is unrelated, but on a multi-core processor even when one core is
running a real-time task, other cores can thrash the cache at will, or
slow down the real-time task by using a shared ressource (for instance
DDR) and starving the core where the real-time task runs. By default the
L2 cache is shared between all cores, you can try and reserve parts of
the cache for each core (check the l2x0 registers documentation to see
how), I tried this on omap4, but it results on worse latencies,
situation may be different on imx6 though. Another problem is that since
the L1 cache is per-core, I believe, and we disable L2 write allocate,
reading on one core memory written on another core results in accesses
at the DDR speed, and not at the cache speed.

All this to say that Xenomai focuses on trying to schedule your driver
interrupts and application threads in a deterministic fashion but it is
your job to make sure that these interrupts and threads do not take too
long a time to execute, because if they do, yes, your application will
not meet its deadlines, but it is not Xenomai's fault.



-- 
Gilles.