The recent introduction of the schedtune cgroup controller has provided
the scheduler with added flexibility in terms of some of it's placement
features. In particular each cgroup under the schedtune controller can
now specify:
1) Whether it needs co-location along with other cgroups
2) Whether it is eligible for scheduler boost (sched_boost_enabled)
3) Whether the kernel can override the boost eligibility when necessary
(sched_boost_no_override)
The scheduler now creates a reserved co-location group at boot. This
group is used to co-locate all tasks that form part of any one of the
cgroups that have co-location enabled. This reserved group can neither
be destroyed nor reused for other purposes. Furthermore, cgroups are
only allowed to indicate their co-location preference once at boot.
Further updates are disallowed.
Since we are now creating co-location groups for an extended period of
time, there are a few other factors to consider when determining the
preferred cluster for the group. We first exclude any tasks in the
group that have not been observed to be running for a significant
amount of time. Secondly we introduce the notion of group up and down
migrate tunables to allow different migration policies than individual
tasks. Lastly we break co-location if a single task in a group exceeds
up-migrate but the total load of the group does not exceed group
up-migrate.
In terms of sched_boost, the scheduler now supports multiple types of
boost. These are:
1) FULL_THROTTLE : Force up-migrate tasks belonging any cgroup that
has the sched_boost_enabled flag turned on. Little
CPUs will only be used when big CPUs can no longer
accommodate tasks. Also up-migrate all RT tasks.
2) CONSERVATIVE : Override the sched_boost_enabled flag for all cgroups
except those that have the sched_boost_no_override
flag set. Force up-migrate all tasks belonging to only
those cgroups that still remain eligible for boost.
RT tasks do not get force up migrated.
3) RESTRAINED : Start frequency aggregation for co-located tasks. This
type of boost does not force up-migrate any task.
Finally the boost API removes ref-counting. This means that there can
only be a single entity using boost at any given time. If multiple
entities are managing boost, they are required to be well behaved so
that they don't interfere with one another. Even for a single client,
it is not possible to switch directly from one boost type to another.
Boost must be first turned off before switching over to a new type.
Change-Id: I8d224a70cbef162f27078b62b73acaa22670861d
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
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