Pavel Machek wrote:
Depending on the ability of the hardware to make software-controlled
power/performance adjustments, this may be useful to select custom
voltages, bus speeds, etc. in desktop/server systems. Various embedded
systems have several parameters that can be set. For example, an XScale
PXA27x could be considered to have six basic power parameters (mainly
cpu run mode and memory and bus dividers) that for the most part
should
This scares me a bit. Is table enough to handle this? I'm afraid that
table will get very large on systems that allow you to do "almost
anything".
Exhaustive tables for all combinations of possible parameters aren't
expected (or practical for many systems as you note). In practice, a
subset of these possible operating points are created and activated over
the lifetime of the system, where the subset is chosen by a system
designer according to the needs of the particular system. It's a matter
for the higher-layer power management software to decide whether to have
in-kernel tables of the possible operating points (as cpufreq does for
various platforms) or whether to require userspace to create only the
ones wanted (as does DPM). There are cpufreq patches for PXA27x
somewhere, for example, and in that case a subset of the supported
operating points (and there are still only about 16 of those even for
such a complicated piece of hardware) are represented in the kernel
tables, choosing one of the possible combinations of memory/bus/etc.
parameters for each unique cpu frequency. Thanks,
--
Todd
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