Re: [RFC] sched: The removal of idle_balance()

From: Srikar Dronamraju
Date: Mon Feb 18 2013 - 03:16:45 EST

> The cache misses dropped by ~23% and migrations dropped by ~28%. I
> really believe that the idle_balance() hurts performance, and not just
> for something like hackbench, but the aggressive nature for migration
> that idle_balance() causes takes a large hit on a process' cache.
> Think about it some more, just because we go idle isn't enough reason to
> pull a runable task over. CPUs go idle all the time, and tasks are woken
> up all the time. There's no reason that we can't just wait for the sched
> tick to decide its time to do a bit of balancing. Sure, it would be nice
> if the idle CPU did the work. But I think that frame of mind was an
> incorrect notion from back in the early 2000s and does not apply to
> today's hardware, or perhaps it doesn't apply to the (relatively) new
> CFS scheduler. If you want aggressive scheduling, make the task rt, and
> it will do aggressive scheduling.

How is it that the normal tick based load balancing gets it correctly while
the idle_balance gets is wrong? Can it because of the different

Thanks and Regards
Srikar Dronamraju

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