Messages in this thread | | | Date | Sun, 13 Jul 2008 11:53:00 +0200 | From | "Dmitry Adamushko" <> | Subject | Re: current linux-2.6.git: cpusets completely broken |
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2008/7/13 Linus Torvalds <torvalds@linux-foundation.org>: > On Sun, 13 Jul 2008, Dmitry Adamushko wrote: >> >> try_to_wake_up() -> ... -> wake_idle() does not see "cpu_active_map". > > You're right. I missed a couple places, because that migrate code not only > ends up using "cpu_is_offline()" instead of "!cpu_online()" (so my greps > all failed), and because it has those online checks in multiple places. > Grr. > > So it would need to change a few other "cpu_is_offline()" calls to > "!cpu_active()" instead (in __migrate_task at a minimum).
it should have checked the result of select_task_rq() in try_to_wake_up() or modify wake_idle() alternatively.
And let me explain one last time why I opposed your 'cpu_active_map' approach.
I do agree that there are likely ways to optimize the hotplug machinery but I have been focused on fixing bugs in a scope of the current framework trying to keep it intact with _minimal_ changes (as it's probably .26 material).
The current way to synchronize with the load-balancer is to attach NULL domains to all sched-domains upon CPU_DOWN_PREPARE and rebuild sched-domains upon CPU_DOWN, effectively making the load-balancer 'blind' (and this way it's workable indeed). Perhaps it's an overkill and something like being proposed by Miao or you should be considered/tried as an alternative.
Even if we place "!cpu_active()" in all the load-balancer-related places (btw., we can also do it with !cpu_online() / cpu_offline() as Miao did with his initial patch) :
(1) common_cpu_mem_hotplug_unplug() -> rebuild_sched_domain() is still called pretty "randomly" (breaking the aforementioned model). At the very least it's an overkill;
(2) sched-domains are broken (at least while CPU_{UP,DOMS} ops. are in progress) and in this state they are still used in a number of places. That's just illogic;
With (2) in place, "cpu_mask_active" acts as a workaround to the existing (broken by CPUSETS) model. If we want "cpu_mask_active" as a primary solution, then the current model should be altered (presumably, we don't need NULL domains any more). Otherwise, it's kind of a strange (illogical) hybrid.
> > Linus >
-- Best regards, Dmitry Adamushko
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