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    Subject[RFC patch 09/27] Add all cpus option to stop machine run
    -allow stop_mahcine_run() to call a function on all cpus. Calling 
    stop_machine_run() with a 'ALL_CPUS' invokes this new behavior.
    stop_machine_run() proceeds as normal until the calling cpu has
    invoked 'fn'. Then, we tell all the other cpus to call 'fn'.

    Signed-off-by: Jason Baron <jbaron@redhat.com>
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    CC: Rusty Russell <rusty@rustcorp.com.au>
    CC: Adrian Bunk <bunk@stusta.de>
    CC: Andi Kleen <andi@firstfloor.org>
    CC: Christoph Hellwig <hch@infradead.org>
    CC: mingo@elte.hu
    CC: akpm@osdl.org
    ---

    include/linux/stop_machine.h | 8 +++++++-
    kernel/stop_machine.c | 31 ++++++++++++++++++++++++-------
    2 files changed, 31 insertions(+), 8 deletions(-)


    Index: linux-2.6-sched-devel/include/linux/stop_machine.h
    ===================================================================
    --- linux-2.6-sched-devel.orig/include/linux/stop_machine.h 2008-04-16 11:07:24.000000000 -0400
    +++ linux-2.6-sched-devel/include/linux/stop_machine.h 2008-04-16 11:13:48.000000000 -0400
    @@ -8,11 +8,17 @@
    #include <asm/system.h>

    #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
    +
    +#define ALL_CPUS ~0U
    +
    /**
    * stop_machine_run: freeze the machine on all CPUs and run this function
    * @fn: the function to run
    * @data: the data ptr for the @fn()
    - * @cpu: the cpu to run @fn() on (or any, if @cpu == NR_CPUS.
    + * @cpu: if @cpu == n, run @fn() on cpu n
    + * if @cpu == NR_CPUS, run @fn() on any cpu
    + * if @cpu == ALL_CPUS, run @fn() first on the calling cpu, and then
    + * concurrently on all the other cpus
    *
    * Description: This causes a thread to be scheduled on every other cpu,
    * each of which disables interrupts, and finally interrupts are disabled
    Index: linux-2.6-sched-devel/kernel/stop_machine.c
    ===================================================================
    --- linux-2.6-sched-devel.orig/kernel/stop_machine.c 2008-04-16 11:07:24.000000000 -0400
    +++ linux-2.6-sched-devel/kernel/stop_machine.c 2008-04-16 11:13:48.000000000 -0400
    @@ -23,9 +23,17 @@ enum stopmachine_state {
    STOPMACHINE_WAIT,
    STOPMACHINE_PREPARE,
    STOPMACHINE_DISABLE_IRQ,
    + STOPMACHINE_RUN,
    STOPMACHINE_EXIT,
    };

    +struct stop_machine_data {
    + int (*fn)(void *);
    + void *data;
    + struct completion done;
    + int run_all;
    +} smdata;
    +
    static enum stopmachine_state stopmachine_state;
    static unsigned int stopmachine_num_threads;
    static atomic_t stopmachine_thread_ack;
    @@ -34,6 +42,7 @@ static int stopmachine(void *cpu)
    {
    int irqs_disabled = 0;
    int prepared = 0;
    + int ran = 0;

    set_cpus_allowed_ptr(current, &cpumask_of_cpu((int)(long)cpu));

    @@ -58,6 +67,11 @@ static int stopmachine(void *cpu)
    prepared = 1;
    smp_mb(); /* Must read state first. */
    atomic_inc(&stopmachine_thread_ack);
    + } else if (stopmachine_state == STOPMACHINE_RUN && !ran) {
    + smdata.fn(smdata.data);
    + ran = 1;
    + smp_mb(); /* Must read state first. */
    + atomic_inc(&stopmachine_thread_ack);
    }
    /* Yield in first stage: migration threads need to
    * help our sisters onto their CPUs. */
    @@ -135,12 +149,10 @@ static void restart_machine(void)
    preempt_enable_no_resched();
    }

    -struct stop_machine_data
    +static void run_other_cpus(void)
    {
    - int (*fn)(void *);
    - void *data;
    - struct completion done;
    -};
    + stopmachine_set_state(STOPMACHINE_RUN);
    +}

    static int do_stop(void *_smdata)
    {
    @@ -150,6 +162,8 @@ static int do_stop(void *_smdata)
    ret = stop_machine();
    if (ret == 0) {
    ret = smdata->fn(smdata->data);
    + if (smdata->run_all)
    + run_other_cpus();
    restart_machine();
    }

    @@ -173,14 +187,17 @@ struct task_struct *__stop_machine_run(i
    struct stop_machine_data smdata;
    struct task_struct *p;

    + mutex_lock(&stopmachine_mutex);
    +
    smdata.fn = fn;
    smdata.data = data;
    + smdata.run_all = (cpu == ALL_CPUS) ? 1 : 0;
    init_completion(&smdata.done);

    - mutex_lock(&stopmachine_mutex);
    + smp_wmb(); /* make sure other cpus see smdata updates */

    /* If they don't care which CPU fn runs on, bind to any online one. */
    - if (cpu == NR_CPUS)
    + if (cpu == NR_CPUS || cpu == ALL_CPUS)
    cpu = raw_smp_processor_id();

    p = kthread_create(do_stop, &smdata, "kstopmachine");
    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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