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    Subject[PATCH v5 1/2] smpboot: allow excluding cpus from the smpboot threads
    Date
    From: Chris Metcalf <cmetcalf@ezchip.com>

    This change allows some cores to be excluded from running the
    smp_hotplug_thread tasks. The motivating example for this is
    the watchdog threads, which by default we don't want to run
    on any enabled nohz_full cores.

    Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
    ---
    include/linux/smpboot.h | 2 ++
    kernel/smpboot.c | 11 ++++++++---
    2 files changed, 10 insertions(+), 3 deletions(-)

    diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
    index d600afb21926..de2f64a98108 100644
    --- a/include/linux/smpboot.h
    +++ b/include/linux/smpboot.h
    @@ -27,6 +27,7 @@ struct smpboot_thread_data;
    * @pre_unpark: Optional unpark function, called before the thread is
    * unparked (cpu online). This is not guaranteed to be
    * called on the target cpu of the thread. Careful!
    + * @exclude_mask: Optional cpumask, specifying cores to exclude.
    * @selfparking: Thread is not parked by the park function.
    * @thread_comm: The base name of the thread
    */
    @@ -41,6 +42,7 @@ struct smp_hotplug_thread {
    void (*park)(unsigned int cpu);
    void (*unpark)(unsigned int cpu);
    void (*pre_unpark)(unsigned int cpu);
    + cpumask_t *exclude_mask;
    bool selfparking;
    const char *thread_comm;
    };
    diff --git a/kernel/smpboot.c b/kernel/smpboot.c
    index c697f73d82d6..8adff4f817fc 100644
    --- a/kernel/smpboot.c
    +++ b/kernel/smpboot.c
    @@ -173,6 +173,9 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
    if (tsk)
    return 0;

    + if (ht->exclude_mask && cpumask_test_cpu(cpu, ht->exclude_mask))
    + return 0;
    +
    td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
    if (!td)
    return -ENOMEM;
    @@ -221,9 +224,11 @@ static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cp
    {
    struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

    - if (ht->pre_unpark)
    - ht->pre_unpark(cpu);
    - kthread_unpark(tsk);
    + if (tsk) {
    + if (ht->pre_unpark)
    + ht->pre_unpark(cpu);
    + kthread_unpark(tsk);
    + }
    }

    void smpboot_unpark_threads(unsigned int cpu)
    --
    2.1.2


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