[RFC PATCH 0/6] Capacity awareness for SCHED_DEADLINE

From: Luca Abeni
Date: Mon May 06 2019 - 01:49:50 EST

From: luca abeni <luca.abeni@xxxxxxxxxxxxxxx>

The SCHED_DEADLINE scheduling policy currently has some issues with
asymmetric CPU capacity architectures (such as ARM big.LITTLE).
In particular, the admission control mechanism does not work correctly
(because it considers all cores to have the same speed of the fastest
core), and the scheduler does not consider the cores' speed when
migrating tasks.

This patchset fixes the issues by explicitly considering the cores'
capacities in the admission control mechanism and in tasks' migration.

In particular, the scheduler is improved so that "heavyweight tasks"
(processes or threads having a runtime that on LITTLE cores becomes
larger than the relative deadline) are scheduled on big cores. This
allows respecting deadlines that are missed by the current scheduler.

Moreover, the migration logic is modified so that "lightweight tasks"
(processes or threads having a runtime that on LITTLE cores is still
smaller than the relative deadline) are scheduled on LITTLE cores
when possible. This allows saving some energy without missing deadlines.

luca abeni (6):
sched/dl: Improve deadline admission control for asymmetric CPU
sched/dl: Capacity-aware migrations
sched/dl: Try better placement even for deadline tasks that do not
sched/dl: Improve capacity-aware wakeup
sched/dl: If the task does not fit anywhere, select the fastest core
sched/dl: Try not to select a too fast core

drivers/base/arch_topology.c | 1 +
include/linux/sched.h | 1 +
include/linux/sched/topology.h | 3 ++
kernel/sched/core.c | 2 +
kernel/sched/cpudeadline.c | 53 ++++++++++++++++++++++--
kernel/sched/deadline.c | 76 ++++++++++++++++++++++++++++------
kernel/sched/sched.h | 16 +++++--
kernel/sched/topology.c | 9 ++++
8 files changed, 143 insertions(+), 18 deletions(-)