On Sat, 2007-07-14 at 14:42 -0400, Mathieu Desnoyers wrote: > Note: (or we could say FIXME) > Is we ever want to check migration pending in assembly code, we will have to > make sure we test the right thread flag bits on each architectures. Care > should > also be taken to check that the thread flags used won't trigger false > positives > in non selective asm thread flag checks. > > FIXME (HOTPLUG) : > > > > /* Affinity changed (again). */ > > > if (!cpu_isset(dest_cpu, p->cpus_allowed)) > > > goto out; > > > > > > on_rq = p->se.on_rq; > > > +#ifdef CONFIG_PREEMPT > > > + if (!on_rq && task_thread_info(p)->migrate_count) > > > + goto out; > > > +#endif > > > > This means that move_task_off_dead_cpu() will spin until the task will be > > scheduled > > on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, > > this > > may > > never happen. > > > > Yes. My idea to fix this issue is the following: > > If a thread has non zero migrate_count, we should still move it to a > different CPU upon hotplug cpu removal, even if this thread resists > migration. Care should be taken to send _all_ such threads to the _same_ > CPU so they don't race for the per-cpu ressources. Does it make sense ? > > We would have to keep the CPU affinity of the threads running on the > wrong CPU until they end their migrate disabled section, so that we can > put them back on their original CPU if it goes back online, otherwise we > could end up with concurrent per-cpu variables accesses. > > (I'll wait for reply before coding a solution for this CPU HOTPLUG > related problem)
What would, aside from technical issues, be the problem with making migration_disable() delay CPU_DOWN until migration_enable()? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
