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    Subject[tip:smp/hotplug] sched/hotplug: Make activate() the last hotplug step
    Commit-ID:  aaddd7d1c740ab3c5efaad7a34650b6dc680c21c
    Gitweb: http://git.kernel.org/tip/aaddd7d1c740ab3c5efaad7a34650b6dc680c21c
    Author: Thomas Gleixner <tglx@linutronix.de>
    AuthorDate: Thu, 10 Mar 2016 12:54:19 +0100
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 6 May 2016 14:58:25 +0200

    sched/hotplug: Make activate() the last hotplug step

    The scheduler can handle per cpu threads before the cpu is set to active and
    it does not allow user space threads on the cpu before active is
    set. Attaching to the scheduling domains is also not required before user
    space threads can be handled.

    Move the activation to the end of the hotplug state space. That also means
    that deactivation is the first action when a cpu is shut down.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Cc: rt@linutronix.de
    Link: http://lkml.kernel.org/r/20160310120025.597477199@linutronix.de
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    include/linux/cpuhotplug.h | 2 +-
    kernel/cpu.c | 15 +++++++++------
    2 files changed, 10 insertions(+), 7 deletions(-)

    diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
    index 9e07468..386374d 100644
    --- a/include/linux/cpuhotplug.h
    +++ b/include/linux/cpuhotplug.h
    @@ -13,11 +13,11 @@ enum cpuhp_state {
    CPUHP_AP_ONLINE,
    CPUHP_TEARDOWN_CPU,
    CPUHP_AP_ONLINE_IDLE,
    - CPUHP_AP_ACTIVE,
    CPUHP_AP_SMPBOOT_THREADS,
    CPUHP_AP_NOTIFY_ONLINE,
    CPUHP_AP_ONLINE_DYN,
    CPUHP_AP_ONLINE_DYN_END = CPUHP_AP_ONLINE_DYN + 30,
    + CPUHP_AP_ACTIVE,
    CPUHP_ONLINE,
    };

    diff --git a/kernel/cpu.c b/kernel/cpu.c
    index d6eeb8c..d948e44 100644
    --- a/kernel/cpu.c
    +++ b/kernel/cpu.c
    @@ -1242,12 +1242,6 @@ static struct cpuhp_step cpuhp_ap_states[] = {
    [CPUHP_AP_ONLINE] = {
    .name = "ap:online",
    },
    - /* First state is scheduler control. Interrupts are enabled */
    - [CPUHP_AP_ACTIVE] = {
    - .name = "sched:active",
    - .startup = sched_cpu_activate,
    - .teardown = sched_cpu_deactivate,
    - },
    /* Handle smpboot threads park/unpark */
    [CPUHP_AP_SMPBOOT_THREADS] = {
    .name = "smpboot:threads",
    @@ -1269,6 +1263,15 @@ static struct cpuhp_step cpuhp_ap_states[] = {
    * The dynamically registered state space is here
    */

    +#ifdef CONFIG_SMP
    + /* Last state is scheduler control setting the cpu active */
    + [CPUHP_AP_ACTIVE] = {
    + .name = "sched:active",
    + .startup = sched_cpu_activate,
    + .teardown = sched_cpu_deactivate,
    + },
    +#endif
    +
    /* CPU is fully up and running. */
    [CPUHP_ONLINE] = {
    .name = "online",
    \
     
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