linux-kernel - [PATCH RFC v0 00/12] Cyclic Scheduler Against RTC

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Date:	Mon, 11 Apr 2016 22:29:08 -0700
From:	"Bill Huey (hui)" <bill.huey@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Cc:	Dario Faggioli <raistlin@...ux.it>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Thomas Gleixner <tglx@...utronix.de>,
	KY Srinivasan <kys@...rosoft.com>,
	Amir Frenkel <frenkel.amir@...il.com>,
	Bdale Garbee <bdale@....com>
Subject: [PATCH RFC v0 00/12] Cyclic Scheduler Against RTC

Hi,

This a crude cyclic scheduler implementation. It uses SCHED_FIFO tasks
and runs them according to a map pattern specified by a 64 bit mask. Each
bit corresponds to an entry into an 64 entry array of
'struct task_struct'. This works single core CPU 0 only for now.

Threads are 'admitted' to this map by an extension to the ioctl() via the
of (rtc) real-time clock interface. The bit pattern then determines when
the task will run or activate next.

The /dev/rtc interface is choosen for this purpose because of its
accessibilty to userspace. For example, the mplayer program already use
it as a timer source and could possibly benefit from being sync to a
vertical retrace interrupt during decoding. Could be an OpenGL program
needing precisely scheduler support for those same handling vertical
retrace interrupts, low latency audio and timely handling of touch
events amognst other uses.

There is also a need for some kind of blocking/yielding interface that can
return an overrun count for when the thread utilizes more time than
allocated for that frame. The read() function in rtc is overloaded for this
purpose and reports overrun events. Yield functionality has yet to be fully
tested.

I apologize for any informal or misused of terminology as I haven't fully
reviewed all of the academic literature regarding these kind of schedulers.
I welcome suggestions and corrects etc

Special thanks to includes...

Peter Ziljstra (Intel), Steve Rostedt (Red Hat), Rik van Riel (Red Hat) for
encouraging me to continue working in the Linux kernel community and being
generally positive and supportive.

KY Srinivasan (formerly Novell now Microsoft) for discussion of real-time
schedulers and pointers to specifics on that topic. It was just a single
discussion but was basically the inspiration for this kind of work.

Amir Frenkel (Palm), Kenneth Albanowski (Palm), Bdale Garbee (HP) for the
amazing place that was Palm, Kenneth for being a co-conspirator with this
scheduler. This scheduler was inspired by performance work that I did
at Palm's kernel group along with discussions with the multimedia team
before HP kill webOS off. Sad and infuriating moment.

Maybe, in a short while, the community will understand the value of these
patches for -rt and start solving the general phenomenon of high performance
multi-media and user interactivity problems more properly with both a
scheduler like this and -rt shipped as default in the near future.

[Also, I'd love some kind of sponsorship to continue what I think is
critical work versus heading back into the valley]

---

Bill Huey (hui) (12):
  Kconfig change
  Reroute rtc update irqs to the cyclic scheduler handler
  Add cyclic support to rtc-dev.c
  Anonymous struct initialization
  Task tracking per file descriptor
  Add anonymous struct to sched_rt_entity
  kernel/userspace additions for addition ioctl() support for rtc
  Compilation support
  Add priority support for the cyclic scheduler
  Export SCHED_FIFO/RT requeuing functions
  Cyclic scheduler support
  Cyclic/rtc documentation

 Documentation/scheduler/sched-cyclic-rtc.txt | 468 ++++++++++++++++++++
 drivers/rtc/Kconfig                          |   5 +
 drivers/rtc/class.c                          |   3 +
 drivers/rtc/interface.c                      |  23 +
 drivers/rtc/rtc-dev.c                        | 161 +++++++
 include/linux/init_task.h                    |  18 +
 include/linux/rtc.h                          |   3 +
 include/linux/sched.h                        |  15 +
 include/uapi/linux/rtc.h                     |   4 +
 kernel/sched/Makefile                        |   1 +
 kernel/sched/core.c                          |  13 +
 kernel/sched/cyclic.c                        | 620 +++++++++++++++++++++++++++
 kernel/sched/cyclic.h                        |  86 ++++
 kernel/sched/cyclic_rt.h                     |   7 +
 kernel/sched/rt.c                            |  41 ++
 15 files changed, 1468 insertions(+)
 create mode 100644 Documentation/scheduler/sched-cyclic-rtc.txt
 create mode 100644 kernel/sched/cyclic.c
 create mode 100644 kernel/sched/cyclic.h
 create mode 100644 kernel/sched/cyclic_rt.h

-- 
2.5.0