• Frederic Weisbecker's avatar
    nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMON · 3451d024
    Frederic Weisbecker authored
    We are planning to convert the dynticks Kconfig options layout
    into a choice menu. The user must be able to easily pick
    any of the following implementations: constant periodic tick,
    idle dynticks, full dynticks.
    
    As this implies a mutual exclusion, the two dynticks implementions
    need to converge on the selection of a common Kconfig option in order
    to ease the sharing of a common infrastructure.
    
    It would thus seem pretty natural to reuse CONFIG_NO_HZ to
    that end. It already implements all the idle dynticks code
    and the full dynticks depends on all that code for now.
    So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
    CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.
    
    On the other hand we want to stay backward compatible: if
    CONFIG_NO_HZ is set in an older config file, we want to
    enable CONFIG_NO_HZ_IDLE by default.
    
    But we can't afford both at the same time or we run into
    a circular dependency:
    
    1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
       CONFIG_NO_HZ
    2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE
    
    We might be able to support that from Kconfig/Kbuild but it
    may not be wise to introduce such a confusing behaviour.
    
    So to solve this, create a new CONFIG_NO_HZ_COMMON option
    which gathers the common code between idle and full dynticks
    (that common code for now is simply the idle dynticks code)
    and select it from their referring Kconfig.
    
    Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
    to it for backward compatibility.
    Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Geoff Levand <geoff@infradead.org>
    Cc: Gilad Ben Yossef <gilad@benyossef.com>
    Cc: Hakan Akkan <hakanakkan@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Kevin Hilman <khilman@linaro.org>
    Cc: Li Zhong <zhong@linux.vnet.ibm.com>
    Cc: Namhyung Kim <namhyung.kim@lge.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    3451d024
fair.c 158 KB