On 11/29/2013 05:36 PM, Gilles Chanteperdrix wrote:
On 11/29/2013 04:10 PM, Carsten Emde wrote:
BTW: Power saving and real-time do not necessarily exclude each other.
If a - still deterministic - but a little longer latency is acceptable,
some light sleep states and a somewhat lower clock frequency may be
allowed which still may result in considerable energy saving. If,
however, the fastest possible real-time response is required, C states
and P states must be disabled (or set to polling and maximum speed,
repsectively) and the power bill must be payed.
Well, I do not fully agree. To be sure that you can clock down the
processor for executing a task which has sufficient time to meet its
deadline, your system must be "time triggered", all the timer events
must be known in advance. Because on a fully dynamic system, you may
make that decision, but a new timer may be scheduled which causes the
system to miss its deadline whereas it would not have missed it if it
had run at full speed.
And a second problem is that you must know the task WCET, which on a
modern system:
- depends on the task frequency;
- depends on the IRQ load.
Again, only a time triggered system seems to make this possible.
--
Gilles.
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
