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Subject[PATCH 0/3] Create sched_select_cpu() and use it in workqueues
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In order to save power, it would be useful to schedule work onto non-IDLE cpus
instead of waking up an IDLE one.

To achieve this, we need scheduler to guide kernel frameworks (like: timers &
workqueues) on which is the most preferred CPU that must be used for these
tasks.

This patchset is about implementing this concept.

The first patch adds sched_select_cpu() routine which returns the preferred cpu
which is non-idle. It accepts max level of sched domain, upto which we can
choose a CPU from. It can accept following options: SD_SIBLING, SD_MC, SD_BOOK,
SD_CPU or SD_NUMA.

Second and Third patch are about adapting this change in workqueue framework.

Earlier discussions over this concept were done at last LPC:
http://summit.linuxplumbersconf.org/lpc-2012/meeting/90/lpc2012-sched-timer-workqueue/

Figures:
--------
Test case 1:
- Performed on TC2 with ubuntu-devel
- Boot TC2 and run
$ trace-cmd record -e workqueue_execute_start

This will trace only the points, where the work actually runs.

Do, this for 150 seconds.

Results:
---------
Domain 0: CPU 0-1
Domain 1: CPU 2-4

Base Kernel: Without my modifications:
-------------------------------------
CPU No. of works run by CPU
----- -----------------------
CPU0: 7
CPU1: 445
CPU2: 444
CPU3: 315
CPU4: 226

With my modifications:
----------------------
CPU No. of works run by CPU
---- -----------------------
CPU0: 31
CPU2: 797
CPU3: 274
CPU4: 86

Test case 2:
-----------
I have created a small module, which does following:
- Create one work for each CPU (using queue_work_on(), so must schedule on that
cpu)
- Above work, will queue "n" works for each cpu with queue_work(). These works
are tracked within the module and results are printed at the end.
This gave similar results, with n ranging from 10 to 1000.

Viresh Kumar (3):
sched: Create sched_select_cpu() to give preferred CPU for power
saving
workqueue: create __flush_delayed_work to avoid duplicating code
workqueue: Schedule work on non-idle cpu instead of current one

arch/arm/Kconfig | 11 +++++++
include/linux/sched.h | 11 +++++++
kernel/sched/core.c | 88 +++++++++++++++++++++++++++++++++++++++------------
kernel/workqueue.c | 36 ++++++++++++++-------
4 files changed, 115 insertions(+), 31 deletions(-)
--
1.7.12.rc2.18.g61b472e




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