lkml.org 
[lkml]   [2011]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread
On Wed, Feb 23, 2011 at 03:44:24AM +0100, Frederic Weisbecker wrote:
> On Tue, Feb 22, 2011 at 05:39:40PM -0800, Paul E. McKenney wrote:
> > +static int rcu_node_kthread(void *arg)
> > +{
> > + int cpu;
> > + unsigned long flags;
> > + unsigned long mask;
> > + struct rcu_node *rnp = (struct rcu_node *)arg;
> > + struct sched_param sp;
> > + struct task_struct *t;
> > +
> > + for (;;) {
> > + wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
> > + kthread_should_stop());
> > + if (kthread_should_stop())
> > + break;
> > + raw_spin_lock_irqsave(&rnp->lock, flags);
> > + mask = rnp->wakemask;
> > + rnp->wakemask = 0;
> > + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> > + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
>
> I may be confused, but shouldn't it be mask >>= 1 instead?

You are not confused, but I sure was! ;-)

> rnp->wakemask is the unioned rdp->grpmask of the cpu(s) for which we woke that
> node thread up. Those mask start from 0, so what you want with the below
> check is to watch if the next CPU in group range is in the wakeup mask by shifting
> to the right.
>
> No?

Not only are you are quite correct, but this bug might well explain the
slowdown in grace-period latency that I was seeing in tests.

Thank you very much!!!

Thanx, Paul

> > + if ((mask & 0x1) == 0)
> > + continue;
> > + preempt_disable();
> > + per_cpu(rcu_cpu_has_work, cpu) = 1;
> > + t = per_cpu(rcu_cpu_kthread_task, cpu);
> > + if (t == NULL) {
> > + preempt_enable();
> > + continue;
> > + }
> > + sp.sched_priority = RCU_KTHREAD_PRIO;
> > + sched_setscheduler_nocheck(t, cpu, &sp);
> > + wake_up_process(t);
> > + preempt_enable();
> > + }
> > + }
> > + return 0;
> > +}


\
 
 \ /
  Last update: 2011-02-23 16:13    [W:0.191 / U:2.584 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site