[PATCH 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

Juri Lelli
2023-03-29T12:55:52Z

Qais reported [1] that iterating over all tasks when rebuilding root
domains for finding out which ones are DEADLINE and need their bandwidth
correctly restored on such root domains can be a costly operation (10+
ms delays on suspend-resume). He proposed we skip rebuilding root
domains for certain operations, but that approach seemed arch specific
and possibly prone to errors, as paths that ultimately trigger a rebuild
might be quite convoluted (thanks Qais for spending time on this!).

To fix the problem

01/06 - Rename functions deadline with DEADLINE accounting (cleanup
suggested by Qais) - no functional change
02/06 - Bring back cpuset_mutex (so that we have write access to cpusets
from scheduler operations - and we also fix some problems
associated to percpu_cpuset_rwsem)
03/06 - Keep track of the number of DEADLINE tasks belonging to each cpuset
04/06 - Create DL BW alloc, free & check overflow interface for bulk
bandwidth allocation/removal - no functional change
05/06 - Fix bandwidth allocation handling for cgroup operation
involving multiple tasks
06/06 - Use this information to only perform the costly iteration if
DEADLINE tasks are actually present in the cpuset for which a
corresponding root domain is being rebuilt

With respect to the RFC posting [2]

1 - rename DEADLINE bandwidth accounting functions - Qais
2 - call inc/dec_dl_tasks_cs from switched_{to,from}_dl - Qais
3 - fix DEADLINE bandwidth allocation with multiple tasks - Waiman,
contributed by Dietmar

This set is also available from

https://github.com/jlelli/linux.git deadline/rework-cpusets

Best,
Juri

1 - https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef-wp2msK0BRk8tq7phqP6ubQ@public.gmane.org/
2 - https://lore.kernel.org/lkml/20230315121812.206079-1-juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org/

Dietmar Eggemann (2):
sched/deadline: Create DL BW alloc, free & check overflow interface
cgroup/cpuset: Free DL BW in case can_attach() fails

Juri Lelli (4):
cgroup/cpuset: Rename functions dealing with DEADLINE accounting
sched/cpuset: Bring back cpuset_mutex
sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
cgroup/cpuset: Iterate only if DEADLINE tasks are present

include/linux/cpuset.h | 12 ++-
include/linux/sched.h | 4 +-
kernel/cgroup/cgroup.c | 4 +
kernel/cgroup/cpuset.c | 232 ++++++++++++++++++++++++++--------------
kernel/sched/core.c | 41 ++++---
kernel/sched/deadline.c | 67 +++++++++---
kernel/sched/sched.h | 2 +-
7 files changed, 240 insertions(+), 122 deletions(-)

--
2.39.2