lkml.org 
[lkml]   [2011]   [May]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: Very high CPU load when idle with 3.0-rc1
    On Mon, May 30, 2011 at 06:46:21PM +0200, Peter Zijlstra wrote:
    > On Mon, 2011-05-30 at 09:23 -0700, Paul E. McKenney wrote:
    >
    > > > @@ -1772,18 +1772,30 @@ static int __init rcu_spawn_kthreads(void)
    > > > {
    > > > int cpu;
    > > > struct rcu_node *rnp;
    > > > + struct task_struct *t;
    > > >
    > > > rcu_kthreads_spawnable = 1;
    > > > for_each_possible_cpu(cpu) {
    > > > per_cpu(rcu_cpu_has_work, cpu) = 0;
    > > > - if (cpu_online(cpu))
    > > > + if (cpu_online(cpu)) {
    > > > (void)rcu_spawn_one_cpu_kthread(cpu);
    > > > + t = per_cpu(rcu_cpu_kthread_task, cpu);
    > > > + if (t)
    > > > + wake_up_process(t);
    > > > + }
    > >
    > > Would it be OK to simplify the code a bit by doing this initial wakeup
    > > in rcu_spawn_one_cpu_kthread() itself? My thought would be to rearrange
    > > rcu_spawn_one_cpu_kthread() as follows:
    >
    > well, no that would get us back to waking a task affine to an offline
    > cpu :-)

    My turn to say d'oh, then!

    But I should be able to move them back in under "if (cpu_online(cpu))",
    right?

    > > > @@ -2209,6 +2221,31 @@ static void __cpuinit rcu_online_kthreads(int cpu)
    > > > }
    > > >
    > > > /*
    > > > + * kthread_create() creates threads in TASK_UNINTERRUPTIBLE state,
    > > > + * but the RCU threads are woken on demand, and if demand is low this
    > > > + * could be a while triggering the hung task watchdog.
    > > > + *
    > > > + * In order to avoid this, poke all tasks once the CPU is fully
    > > > + * up and running.
    > > > + */
    > > > +static void __cpuinit rcu_online_kthreads(int cpu)
    > > > +{
    > > > + struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
    > > > + struct rcu_node *rnp = rdp->mynode;
    > > > + struct task_struct *t;
    > > > +
    > > > + t = per_cpu(rcu_cpu_kthread_task, cpu);
    > > > + if (t)
    > > > + wake_up_process(t);
    > > > +
    > > > + t = rnp->node_kthread_task;
    > > > + if (t)
    > > > + wake_up_process(t);
    > > > +
    > > > + rcu_wake_one_boost_kthread(rnp);
    > >
    > > Interesting... So we are really awakening them twice, once at creation
    > > time to get them to sleep interruptibly, and a second time when the CPU
    > > comes online.
    > >
    > > What does this second set of wake_up_process() calls do?
    >
    > Ah, not so, see the initial one is conditional on cpu_online() and will
    > fail for the CPU_UP_PREPARE case, this new function will be ran from
    > CPU_ONLINE to then issue the first wakeup.
    >
    > The distinction comes from the initialize while cpus are already running
    > vs hotplug.

    OK, got it.

    Thanx, Paul


    \
     
     \ /
      Last update: 2011-05-30 23:33    [W:0.100 / U:58.304 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site