Messages in this thread | | | Date | Sat, 3 Feb 2007 16:31:22 -0800 | From | "Paul E. McKenney" <> | Subject | Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug |
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On Sat, Feb 03, 2007 at 11:27:24PM +0100, Rafael J. Wysocki wrote: > On Saturday, 3 February 2007 01:01, Pavel Machek wrote: > > Hi! > > > > > > > > static int _cpu_down(unsigned int cpu) > > > > > > { > > > > > > int err; > > > > > > struct task_struct *p; > > > > > > cpumask_t old_allowed, tmp; > > > > > > > > > > > > if (num_online_cpus() == 1) > > > > > > return -EBUSY; > > > > > > > > > > > > if (!cpu_online(cpu)) > > > > > > return -EINVAL; > > > > > > > > > > > > if (freeze_processes()) { > > > > > > err = -EBUSY; > > > > > > goto out_freeze_notify_failed; > > > > > > } > > > > > > err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE, > > > > > > (void *)(long)cpu); > > > > > > > > > > yeah. This all looks so nice that i almost cannot believe it's true :-) > > > > > > > > Well, it turns out that maybe it is in fact untrue. :-/ > > > > > > > > I need to look at all uses of PF_NOFREEZE -- as I understand the > > > > code, processes marked PF_NOFREEZE will continue running, potentially > > > > interfering with the hotplug operation. :-( > > > > > > > > I will pass my findings on to this list. > > > > > > Well, I did it some time ago, although not very thoroughly. > > > > > > AFAICS there are not so many, but one that stands out is the worker threads. > > > We needed two of them to actually go to sleep, so now it's possible to create > > > a "freezeable workqueue" the worker thread of which will not set PF_NOFREEZE, > > > but currently this is only used by XFS. > > > > We should slowly move as workqueues to freezeable ones... Having too > > much stuff NOFREEZE is evil, even for swsusp. > > On the other hand, some of the workqueues may be necessary for saving the image > (still, I have no examples ;-)).
In any case, getting CPU hotplug working is probably first priority.
That said, I am testing a patch that (hopefully) gets rid of the RCU-boost and rcutorture NOFREEZE tasks. Every little bit will help.
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