Re: [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-periodinitialization into a kthread

[Peter Zijlstra]

On Thu, 2012-08-30 at 11:18 -0700, Paul E. McKenney wrote:
> +static int rcu_gp_kthread(void *arg)
> +{
> +       unsigned long flags;
> +       struct rcu_data *rdp;
> +       struct rcu_node *rnp;
> +       struct rcu_state *rsp = arg;
> +
> +       for (;;) {
> +
> +               /* Handle grace-period start. */
> +               rnp = rcu_get_root(rsp);
> +               for (;;) {
> +                       wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
> +                       if (rsp->gp_flags)
> +                               break;
> +                       flush_signals(current);
> +               }
> +               raw_spin_lock_irqsave(&rnp->lock, flags); 

You're in a kthread, it should be impossible for IRQs to be disabled
here, no? Similar for most (all) other sites in this function.

Using the unconditional IRQ disable/enable is generally faster.
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