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    Subject[PATCH tip/core/rcu 14/17] rcutorture: Adjust number of reader kthreads per CPU-hotplug operations
    Date
    Currently, rcutorture provisions rcu_torture_reader() kthreads based
    on the initial number of CPUs. This can be problematic when CPU hotplug
    is enabled, as a system with a very large number of CPUs will provision
    a very large number of rcu_torture_reader() kthreads. All of these
    kthreads will continue running even if the CPU-hotplug operations result
    in only one remaining online CPU. This can result in all sorts of strange
    artifacts due simply to massive overload.

    This commit therefore causes the rcu_torture_reader() kthreads to start
    blocking as the number of online CPUs decreases. This is accomplished
    by numbering these kthreads, and having each check to make sure that the
    number of online CPUs is at least as large as its assigned number.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcu/rcutorture.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
    index ac487ea8d245..50015b78a43f 100644
    --- a/kernel/rcu/rcutorture.c
    +++ b/kernel/rcu/rcutorture.c
    @@ -1400,6 +1400,8 @@ static int
    rcu_torture_reader(void *arg)
    {
    unsigned long lastsleep = jiffies;
    + long myid = (long)arg;
    + int mynumonline = myid;
    DEFINE_TORTURE_RANDOM(rand);
    struct timer_list t;

    @@ -1419,6 +1421,8 @@ rcu_torture_reader(void *arg)
    schedule_timeout_interruptible(1);
    lastsleep = jiffies + 10;
    }
    + while (num_online_cpus() < mynumonline && !torture_must_stop())
    + schedule_timeout_interruptible(HZ / 5);
    stutter_wait("rcu_torture_reader");
    } while (!torture_must_stop());
    if (irqreader && cur_ops->irq_capable) {
    @@ -2063,7 +2067,7 @@ static void rcu_test_debug_objects(void)
    static int __init
    rcu_torture_init(void)
    {
    - int i;
    + long i;
    int cpu;
    int firsterr = 0;
    static struct rcu_torture_ops *torture_ops[] = {
    @@ -2169,7 +2173,7 @@ rcu_torture_init(void)
    goto unwind;
    }
    for (i = 0; i < nrealreaders; i++) {
    - firsterr = torture_create_kthread(rcu_torture_reader, NULL,
    + firsterr = torture_create_kthread(rcu_torture_reader, (void *)i,
    reader_tasks[i]);
    if (firsterr)
    goto unwind;
    --
    2.17.1
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