[git pull request] ACPI Processor Aggregator Device Driver

[Len Brown]

Hi Linus,

please pull from: 

git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6.git acpi-pad

We believe that this driver is useful in this form, particularly since
it can be available in Linux as this underlying feature
is rolled out by platform vendors.

Per the commit message below, Vaidy and PeterZ have proposed
making the scheduler smarter, and they do not agree that this
driver should be upstream before those enhancements are ready.

So I've put this driver on its own branch to let you decide
if it should go upstream now or not.

This will update the files shown below.

thanks!

--
Len Brown
Intel Open Source Technology Center


ps. individual patches are available on linux-acpi@xxxxxxxxxxxxxxx
and a consolidated plain patch is available here:
http://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/2.6.31/acpi-acpi-pad-20090521-2.6.31-rc4.diff.gz

 MAINTAINERS             |    8 +
 drivers/acpi/Kconfig    |   11 +
 drivers/acpi/Makefile   |    2 +
 drivers/acpi/acpi_pad.c |  514 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 535 insertions(+), 0 deletions(-)
 create mode 100644 drivers/acpi/acpi_pad.c

through these commits:

Shaohua Li (1):
      ACPI: create Processor Aggregator Device driver

with this log:

commit 8e0af5141ab950b78b3ebbfaded5439dcf8b3a8d
Author: Shaohua Li <shaohua.li@xxxxxxxxx>
Date:   Mon Jul 27 18:11:02 2009 -0400

    ACPI: create Processor Aggregator Device driver
    
    ACPI 4.0 created the logical "processor aggregator device" as
    a mechinism for platforms to ask the OS to force otherwise busy
    processors to enter (power saving) idle.
    
    The intent is to lower power consumption to ride-out
    transient electrical and thermal emergencies,
    rather than powering off the server.
    
    On platforms that can save more power/performance via P-states,
    the platform will first exhaust P-states before forcing idle.
    However, the relative benefit of P-states vs. idle states
    is platform dependent, and thus this driver need not know
    or care about it.
    
    This driver does not use the kernel's CPU hot-plug mechanism
    because after the transient emergency is over, the system must
    be returned to its normal state, and hotplug would permanently
    break both cpusets and binding.
    
    So to force idle, the driver creates a power saving thread.
    The scheduler will migrate the thread to the preferred CPU.
    The thread has max priority and has SCHED_RR policy,
    so it can occupy one CPU.  To save power, the thread will
    invoke the deep C-state entry instructions.
    
    To avoid starvation, the thread will sleep 5% of the time
    time for every second (current RT scheduler has threshold
    to avoid starvation, but if other CPUs are idle,
    the CPU can borrow CPU timer from other,
    which makes the mechanism not work here)
    
    Vaidyanathan Srinivasan has proposed scheduler enhancements
    to allow injecting idle time into the system.  This driver doesn't
    depend on those enhancements, but could cut over to them
    when they are available.
    
    Peter Z. does not favor upstreaming this driver until
    the those scheduler enhancements are in place.  However,
    we favor upstreaming this driver now because it is useful
    now, and can be enhanced over time.
    
    Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
    NACKed-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
    Cc: Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx>
    Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
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