On Mon, Nov 03, 2014 at 04:54:37PM +0000, Vincent Guittot wrote:

This patchset consolidates several changes in the capacity and the usage
tracking of the CPU. It provides a frequency invariant metric of the usage of
CPUs and generally improves the accuracy of load/usage tracking in the
scheduler. The frequency invariant metric is the foundation required for the
consolidation of cpufreq and implementation of a fully invariant load tracking.
These are currently WIP and require several changes to the load balancer
(including how it will use and interprets load and capacity metrics) and
extensive validation. The frequency invariance is done with
arch_scale_freq_capacity and this patchset doesn't provide the backends of
the function which are architecture dependent.

As discussed at LPC14, Morten and I have consolidated our changes into a single
patchset to make it easier to review and merge.

During load balance, the scheduler evaluates the number of tasks that a group
of CPUs can handle. The current method assumes that tasks have a fix load of
SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
This assumption generates wrong decision by creating ghost cores or by
removing real ones when the original capacity of CPUs is different from the
default SCHED_CAPACITY_SCALE. With this patch set, we don't try anymore to
evaluate the number of available cores based on the group_capacity but instead
we evaluate the usage of a group and compare it with its capacity.

This patchset mainly replaces the old capacity_factor method by a new one and
keeps the general policy almost unchanged. These new metrics will be also used
in later patches.

The CPU usage is based on a running time tracking version of the current
implementation of the load average tracking. I also have a version that is
based on the new implementation proposal [1] but I haven't provide the patches
and results as [1] is still under review. I can provide change above [1] to
change how CPU usage is computed and to adapt to new mecanism.

Change since V8
 - reorder patches

I think the patch set is in a good shape. I have got few comments and
suggestions mostly minor things and things related to naming to the
first 7 patches. I haven't found any problems with the code itself. I
haven't tested it yet though. The last three patches I have a few
questions for.

Morten