System slow down from udev

[Yinghai Lu]

Raphael:

Found one commit in your linus-pm cause user space very slow...
at least from udev start...

bisect to

ac212b6980d8d5eda705864fc5a8ecddc6d6eacc is the first bad commit
commit ac212b6980d8d5eda705864fc5a8ecddc6d6eacc
Author: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Date:   Fri May 3 00:26:22 2013 +0200

    ACPI / processor: Use common hotplug infrastructure

    Split the ACPI processor driver into two parts, one that is
    non-modular, resides in the ACPI core and handles the enumeration
    and hotplug of processors and one that implements the rest of the
    existing processor driver functionality.

    The non-modular part uses an ACPI scan handler object to enumerate
    processors on the basis of information provided by the ACPI namespace
    and to hook up with the common ACPI hotplug infrastructure.  It also
    populates the ACPI handle of each processor device having a
    corresponding object in the ACPI namespace, which allows the driver
    proper to bind to those devices, and makes the driver bind to them
    if it is readily available (i.e. loaded) when the scan handler's
    .attach() routine is running.

    There are a few reasons to make this change.

    First, switching the ACPI processor driver to using the common ACPI
    hotplug infrastructure reduces code duplication and size considerably,
    even though a new file is created along with a header comment etc.

    Second, since the common hotplug code attempts to offline devices
    before starting the (non-reversible) removal procedure, it will abort
    (and possibly roll back) hot-remove operations involving processors
    if cpu_down() returns an error code for one of them instead of
    continuing them blindly (if /sys/firmware/acpi/hotplug/force_remove
    is unset).  That is a more desirable behavior than what the current
    code does.

    Finally, the separation of the scan/hotplug part from the driver
    proper makes it possible to simplify the driver's .remove() routine,
    because it doesn't need to worry about the possible cleanup related
    to processor removal any more (the scan/hotplug part is responsible
    for that now) and can handle device removal and driver removal
    symmetricaly (i.e. as appropriate).

    Some user-visible changes in sysfs are made (for example, the
    'sysdev' link from the ACPI device node to the processor device's
    directory is gone and a 'physical_node' link is present instead
    and a corresponding 'firmware_node' is present in the processor
    device's directory, the processor driver is now visible under
    /sys/bus/cpu/drivers/ and bound to the processor device), but
    that shouldn't affect the functionality that users care about
    (frequency scaling, C-states and thermal management).

    Tested on my venerable Toshiba Portege R500.

    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
    Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Toshi Kani <toshi.kani@xxxxxx>

:040000 040000 24925fd62fd97295be145d62f8d849004eeca284
30c7f7f9ff26f17eaabf1770eb7d0b69c2767ba8 M    drivers
:040000 040000 8374b2dcd64a21abc1f65d3c7779ffa71adb01ba
9375e83719e970b6f4b9a61fe6080bd638dfc51c M    include
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