lkml.org 
[lkml]   [2011]   [Jan]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC][PATCH 17/18] sched: Move the second half of ttwu() to the remote cpu
    On 01/04, Peter Zijlstra wrote:
    >
    > Now that we've removed the rq->lock requirement from the first part of
    > ttwu() and can compute placement without holding any rq->lock, ensure
    > we execute the second half of ttwu() on the actual cpu we want the
    > task to run on.

    Damn. I am reading this patch back and forth, many times, and
    I am not able to find any problem. So sad!

    I'll try to read it once again with the fresh head, though ;)
    I also have a couple of very minor nits... In particular, perhaps
    TASK_WAKING can die...

    Just one question for today,

    > try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
    > {
    > - int cpu, this_cpu, success = 0;
    > unsigned long flags;
    > - struct rq *rq;
    > -
    > - this_cpu = get_cpu();
    > + int cpu, success = 0;
    >
    > smp_wmb();
    > raw_spin_lock_irqsave(&p->pi_lock, flags);
    > if (!(p->state & state))
    > goto out;
    >
    > + success = 1; /* we're going to change ->state */
    > cpu = task_cpu(p);
    >
    > - if (p->on_rq) {
    > - rq = __task_rq_lock(p);
    > - if (p->on_rq)
    > - goto out_running;
    > - __task_rq_unlock(rq);
    > - }
    > + if (p->on_rq && ttwu_remote(p, wake_flags))
    > + goto stat;
    > +
    > + p->sched_contributes_to_load = !!task_contributes_to_load(p);
    > + p->state = TASK_WAKING;
    >
    > #ifdef CONFIG_SMP
    > + /*
    > + * If the owning (remote) cpu is still in the middle of schedule() with
    > + * this task as prev, wait until its done referencing the task.
    > + */
    > while (p->on_cpu)
    > cpu_relax();

    Don't we need rmb() after that?

    No, I am not saying it _is_ needed. I am asking.

    (but need_migrate_task() can avoid on_cpu+rmb afaics)

    Oleg.



    \
     
     \ /
      Last update: 2011-01-05 22:19    [W:0.045 / U:0.100 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site