Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 15 Dec 2006 17:24:16 +0100 | From | Ingo Molnar <> | Subject | Re: + schedule_on_each_cpu-use-preempt_disable.patch added to -mm tree |
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* Andrew Morton <akpm@osdl.org> wrote:
> > > for_each_online_cpu(cpu) { > > > INIT_WORK(per_cpu_ptr(works, cpu), func); > > > __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), > > > per_cpu_ptr(works, cpu)); > > > } > > > - mutex_unlock(&workqueue_mutex); > > > + preempt_enable(); > > > > Why not cpu_hotplug_lock()? > > > > Because the workqueue code was explicitly switched over to > per-subsystem cpu-hotplug locking. > > Because lock_cpu_hotplug() is a complete turkey, source of deadlocks > and overall bad idea.
not in the locking model i outlined earlier, which would turn it into a read-lock in essence.
> This is actually a pretty simple problem. A subsystem has per-cpu > reosurces, and it needs to lock them while using them. duh. We know > how to do that sort of thing. But because the first implementation of > lock_cpu_hotplug() was conceived with magical properties, we seem to > think we need to retain magical properties. We don't...
actually, we use two things here: cpu_online_map and the per-cpu keventd workqueues. cpu_online_map is pretty much attached to the CPU hotplug subsystem so it would be quite natural to use cpu_hotplug_read_lock() for that.
so i disagree that CPU hotplug locking should be per-subsystem. We should have one lightweight and scalable primitive that protects cpu_online_map use, and that same primitive can be used to protect other per-CPU resources too.
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