Messages in this thread | | | Date | Thu, 2 Jul 2015 09:05:39 +0800 | From | Yuyang Du <> | Subject | Re: [PATCH?] Livelock in pick_next_task_fair() / idle_balance() |
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Hi Mike,
On Thu, Jul 02, 2015 at 10:05:47AM +0200, Mike Galbraith wrote: > On Thu, 2015-07-02 at 07:25 +0800, Yuyang Du wrote: > > > That being said, it is also obvious to prevent the livelock from happening: > > idle pulling until the source rq's nr_running is 1, becuase otherwise we > > just avoid idleness by making another idleness. > > Yeah, but that's just the symptom, not the disease. Better for the idle > balance symptom may actually be to only pull one when idle balancing. > After all, the immediate goal is to find something better to do than > idle, not to achieve continual perfect (is the enemy of good) balance. > Symptom? :)
You mean "pull one and stop, can't be greedy"? Right, but still need to assure you don't make another idle CPU (meaning until nr_running == 1), which is the cure to disease.
I am ok with at most "pull one", but probably we stick to the load_balance() by pulling an fair amount, assuming load_balance() magically computes the right imbalance, otherwise you may have to do multiple "pull one"s.
Thanks, Yuyang
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